So I've gone in a custom with the full build with the ROA vs GLP. The GLP compromises 20AP off of ROA at the cost of 5 mins. That is 5 mins means you get the GLP AP around 15-18 mins since most people finish the ROA around 10-13 mins. Having that extra AP with the Active damage 3 mins earlier(To make up cost difference) makes a huge difference. Now ofcourse some argue for the ROA Scaling power, but in the current meta not all games are lasting that long. The GLP adds extra cc to the kit in the team fighting meta which is great.

Lissandra also still keeps the one shotting power because in the custom game I compared the damage of the full lissandra combo (2Qs 1E 1W 1R 1Auto), and the GLP matches the exact damage with the active for the extra 20 ap off the ROA. So you still can one shot squishies if you get on them.

If you like the scaling ways take 20% cdr with Hextech GLP + Zhonya early. Lissandra needs full 40% cdr to put out her dps in fights. If you want to be squishy and explosive early then take 10% CDR and replace rest with AP and build Morello + Zhonya. This has a stronger early game but the scaling is not that great.

You want to always take thunderlords for the sheer burst damage on squishies later and its also great for trading in lane. Deathfire is also an option but you will have a weak laning phase with that. However late game Deathfire is quite good in team fights for consistent dps.

Against champions like Ahri, Twisted Fate (All the green threat levels). You should be driving ahead in farm from them. As Lissandra the moment you hit 6 you want to all in the enemy to get kills. If they play too safe, just shove your lane and roam with your ultimate. Always buy pinks when ahead to give you that gank security when engaging. If you see that enemy Mid follows your roams, fake roam to your pink wards and gank them.

Just focus on farming and staying even. You have to wait for ganks in these situations. Keep your jungler updated on your E and R cooldowns to collaborate good ganks. With Lissandra most ganks are succesful even if the nemy has flash.

Just focus on farming to stay relavant. If enemy laner gets ahead, tower hug and wait for ganks. Do not try to farm if they zone you, simply wait under tower. Levels is more important than cs if you will die for it. You will take over in team fights with your cc.

As lissandra you're always eyeing squishy carries in teamfights. Theres two ways to play it out. If you are really fed then you can simply E in to start the fight and burst down the ADC and then zhonyas for your team to catch up. If you're moderately fed and trust your team, E into the frontline and instantly W. When the enemy starts to jump on you, just ult yourself and you should do ridiculous AOE damage. By now the team should have caught up with you to close out the fight.

The other method is to wait for the teamfight to break out while stalking enemy carries. When the fight breaks out you can use your claw to dive the carries going unnoticed.

If they have a heavy shield/heals comp and you're unable to one shot carries, just stick with your frontline and chip away on the enemy tanks. If you have liandry's Torment done then this should be no problem.

Take ignite in the yellow/green threat matchups. Take teleport against Red threat matchups.
Teleport is usually better to make plays. Go ignite if you are confident it will get you fed to carry game without teleport ganks.

Theres 3 Main things to touch upon regarding Lissandra Mechanics:

Escaping/Fleeing: When you are in danger use your E towards safety. While the claw is going, move towards the enemies and press W and E right after to snare them and blink to your claw instantly to make a clean escape. If the enemy you're running from has hard cc try to reactivate your E as soon as you see the cc come out or see them come close enough in range.

Full Combo Rotation: Whenever possible flash W onto your target, then use Q once and use your ultimate and use Q again. (Use your autoattacks in between if Q is not off cooldown) By now when the cc is over just use your claw to follow their flashes/dashes to close out the kill. Squeese in Qs and Autos whenever you can while fighting to maximise your DPS.

Waveclearing: When underpressure and near your tower, use Q-E to do a quick waveclear. If not under pressure use Q and W on the wave to clear it fast. Multiple Q's can also be alright to clear waves if you're saving the blink and cc for a kill or an escape. When holding tower Q-E is the best method since its the fastest waveclear you've got to stop enemy's from sieging your tower.

Lissandra is a strong control mage which good waveclear to allow you to dictate the pace of the game. If your team falls behind request them to play safe as you can easily stall the game out with your waveclear and force the enemy team to dive you due to your anti siege kit. When ahead start roaming. With all the cc lissandra offers most of your ganks will be very impactful even if your laners are behind.