Champion strength as a mage comes from her incredible amount of utility and AoE damage from her abilities, being able to engage with Glacial Path and Frozen Tomb to lock down several enemies at once, followed by Ring of Frost and Ice Shard. This along with her passive, Iceborn, allows her to mitigate some of her mana issues during the laning phase.
Iceborn's cooldown will be 17 seconds instead of 18 if the you hit an enemy with Ice Shard.
When in lane, try to cast Ice Shard on minions to hit an enemy champion behind them. This is your main method of harassment and zoning, opening up a kill opportunity at level 6 or when Frozen Tomb is ready.
Ice Shard's mana cost is abnormally high for a mage's most used ability; do not use it too recklessly at early levels.
It is a good idea to pace your usage of the spell so that you can farm minions effectively and damage your lane opponent while also maintaining your mana through Iceborn.
Casting Glacial Path and then running in the opposite direction will leave your enemies uncertain which way you will actually go.
All of Champion basic abilities are skill shots or have very short range. Frozen Tomb solves this by ensuring that the enemy is immobile while you damage them with your other abilities.
Try not to overlap the crowd control from Frozen Tomb with that of Ring of Frost. Pacing them out will make sure your main target stays put for a longer period of time (up to 3 seconds when timed correctly).
While she is primarily a utility mage, Lissandra can drop a squishy enemy instantly if done correctly. In the best case scenario, you will start with Frozen Tomb, followed by Ice Shard and Ring of Frost as Frozen Tomb ends to maximize CC lockdown. Use Glacial Path to finish or if the enemy tries to run away or to get away yourself.
Try to cast Ice Shard in a position where it would hit the most enemies to maximize the damage.
In team fights, try to use Frozen Tomb on the champion in the center of the enemy team to deal damage to as many enemies as possible.
Alternatively, you can use Glacial Path to blink to the center of the enemy team and use Ring of Frost to root them immediately giving your team free hits and then self-targeting Frozen Tomb when the root is finished to prevent the enemy team from retreating or retaliating.
Additionally, if you have a Zhonya's Hourglass (which is recommended with Champion ability to ult herself, effectively providing 5 seconds of invulnerability when used in sequence with the active), it would be possible to Glacial Path into the enemy team, use Frozen Tomb to lock down a high priority target along with Ring of Frost, allowing your team to follow up. The reason for having a Zhonya's Hourglass is so that Lissandra can avoid retaliation for using her ult on an enemy. This tactic does require good communication, however, as it is risky but highly rewarding if executed properly.
Frozen Tomb is one of the most powerful disables in the game, choose your target carefully.
When a squishy enemy is out of position, use Glacial Path and lock him down with Frozen Tomb. This allows your team to finish off a threat before you allow it to deal damage.
Frozen Tomb can also be used on the enemy initiator as they will be damaged and slowed by the ice.
With enough items, Frozen Tomb can be used on herself in the middle of the enemy team to deal damage and apply a crucial slow to them.
Ring of Frost will reduce the cooldown on Iceborn by the number of enemies hit. If an entire minion wave is hit, this will reduce Iceborn's cooldown by six or seven seconds (depending on if a cannon/super minion is present).
Glacial Path is a very good skill to pass through walls and run away from enemies. Note however, that Glacial Path does not grant vision in the fog of war.
If Lissandra uses Glacial Path, but is then CC'd in a way that prevents her from using her skills or moving while Glacial Path is still traveling, she will not be able to teleport to its location, leaving her without an escape. Be wary of CC heavy champs.
If you are facing a pure melee champion who is heavily reliant on being within melee range to do damage such as Singed, Riven, Renekton or Yasuo, you can max out Ring of Frost for the cooldown reduction. The mana cost is much lower and the damage scales better than Ice Shard. Utilizing this method will allow you to punish opponents or zone them with the threat of a guaranteed Ice Shard.
Lissandra excels when against melee champions due to her ability to kite with Ice Shard. If a melee opponent goes in to last hit, using Ice Shard will almost ensure that they receive damage as they won't be able to react in time (although this can become risky due to Ice Shard's high mana cost. It should not be done too often to conserve mana.)
Lissandra is a very strong pick against many assassins, particularly Zed and Katarina as she can ult herself or them to negate their damage. Assassins often rely on combining their abilities, which Lissandra excels at disrupting. Against champions like Talon, this becomes more skill based as champions like him who are equipped with silences will make it difficult to react and leave you vulnerable.
Rod of Ages is an item that offers Champion decent stats. The health adds to her survivability and allows her to be at close range longer, the mana combined with Iceborn will solve her mana issues, and the ability power is naturally beneficial.
Instead of Rod of Ages, picking up an Athene's Unholy Grail will more than solve her mana issues, give a fair amount of magic resistance, give a generous amount of CDR, and a decent amount of AP to boot.
Morellonomicon's mana regeneration is not as overwhelmingly high, while being cheaper and offering slightly higher ability power. However, it does not give any magic resistance.
Unlike most mage champions, Lissandra focuses more on kiting and disabling enemies rather than dealing raw damage. Consider buying an Ionian Boots of Lucidity for some early game cooldown reduction and later sell it for a Sorcerer's Shoes once you have an item with higher cooldown reduction.
If you are building tanky in order to dive in the enemy team, you can also consider Mercury's Treads, as the tenacity will prove very useful given her short range.
Alternatively, Lissandra can be built as a tank, using Glacial Path to wade into the middle of a teamfight and Ring of Frost to root the enemy team. This build makes excellent use of Cooldown reduction and acknowledges her lower than average AP ratios.
While she is a utility mage Lissandra still deals a lot of magic damage. By the late or mid game Void Staff will be needed to effectively damage fighters/bruisers and tanks.
Liandry's Torment in particular synergizes well with her abilities, most of them being able to impair movement and apply the stronger burn.
Rylai's Crystal Scepter is a decent item on Lissandra. It gives a good amount of ability power and health, and its passive further increases the magnitude of Champion crowd control abilities. Note that Ice Shard is a single-target ability when cast and an area of effect ability when it hits and shatters, so it fully benefits from Rylai's Crystal Scepter's passive on the first hit, and has reduced effect on the shatter.
When Lissandra is ganking, keep an eye out for her Glacial Path as she can blink to its position. Stay clear of it as she can follow-up with her Ring of Frost to snare you when she blinks.
Wielding an immense amount of crowd control and impressive mobility with Glacial Path, Lissandra is a very dangerous roamer. Make sure to keep a ward on any lane she is near, and play defensive if you do not see her.
Champion abilities have a rather short range so try to distance yourself away to prevent yourself from being slowed, snared or stunned.
Team fights are where Lissandra shines in particular. If you think you're a high priority to the enemy team, avoid being stunned by Frozen Tomb and rooted by Ring of Frost.
Lissandra is a very tricky champion to gank or even lock down in a teamfight, due to Glacial Path's long blink, however, she also uses this as her initiation, so bring her down when she lacks her escape.
If you apply a stun, snare, suppress, knock up or silence on her after she throws out the claw she will not be able to blink and may even lose any chance to do so, leaving her very vulnerable.
Champion immense amount of crowd control makes it very tricky to even properly engage on her for a duel. Try doing so when she has at least thrown out two different spells. Her Glacial Path is her escape, and her Ring of Frost are what make her so difficult to gank. If both of these are on cooldown, she is incredibly open to engages.
Due to her high amount of AoE damage, Lissandra is very good at pushing waves. Don't leave her unchecked in a lane for too long.
Ice Shard has a short range, but extends by 100 units if it hits a target. Try to avoid your minions as this is Champion primary means of harass and is part of the reason why she is so effective against melee champions in lane. She can also sustain this method for a long time despite Ice Shard's high mana cost thanks to her passive, Iceborn.
If you are melee, be careful when you are trying to gap close her, as she can simply use Ring of Frost to snare you and walk away. Try to bait it, as it has a moderate cooldown early on.
The ice from Frozen Tomb takes a short time to expand. If you are fast enough, you may be able to move away from it and not take the damage, as long as you are not the primary target.
Being grouped up in tight areas or being close together in general is dangerous due to Champion high amount of AoE damage and CC, specifically Frozen Tomb, as it deals a decent amount of damage for players without a decent amount of MR and creates a detrimental slowing field.
By combining Frozen Tomb and Zhonya's Hourglass, Lissandra can stay invulnerable for a total of 5 seconds. Either try to be fast enough to stop her from chaining them, or focus on her team, as it also means she can't do anything for 5 seconds. Simply waiting for the effect to end will give a lot of time for her team to act, so avoid overstaying unless she is clearly out of position.
This trick will also make sure her Ice Shard and Ring of Frost are ready to use so be mindful of this in a duel.
Do not carelessly dive Lissandra, as she can use Frozen Tomb to either protect herself or lock you under her tower while she escapes with Glacial Path or burst you down depending on the situation.
Glacial Path has a moderately high cooldown, especially at early levels and without it, Lissandra has below average mobility. Take advantage of this.