I'll share a couple for a few of my favorites.
As
, there are two distinct playstyles that you can use to adapt to your enemy. If they've got a short ranged assassin or burst mage that can easily all in you,
or
for example, keep your distance and poke with your range. Don't go anywhere near them, even to use your passive. A bit of extra damage isn't worth you dying for. Basically just always keep your distance, and stay in the back line. The second is to use against other long ranged champions, champions like
or
. With this you're going to be in their face, tossing autos between Q's and doing your best to dodge their spells. Your passive will help you win trades even if you get hit by the enemies spells.
As
top lane, you'll often run into champions that, after an MR item or two, you straight up can't kill. Champions like
. but that doesn't mean you don't still counter them. It's not all about killing them, it's about making sure you're farming well while they're not. So even if it seems like you'll run OOM before you kill them, keep harassing at all times. If done well, I assure you you'll have at least double their farm by the end of lane phase. For squishier laners, it often takes only one ulted Q to make them think twice about staying in lane. Once they back, be sure to look out for their return and slap them with an ulted Q as they're walking back to lane. And last but not least, Karma is deceptively durable for the amount of damage and lack of tank items she builds. Playing her as a poke/kite mage is all about looking like an easy kill, then dancing out of their reach with slows, snares, and your shield and MS buff. Poke them when they refuse to engage on you, kill them when they engage on you. Don't be afraid to fight under enemy tower.
As
mid lane always throw a Q and a seed between the casters and melee minions when your enemy gets near for farm. Doing this either keeps them away from farming or they take free damage. Much like Karma top, you can easily fight under enemy towers. Use your superior range and plants to do damage from beyond the tower's range, or within it and have your plants tank for you. Again, like Karma top, if you see an enemy coming back into lane after backing, slap them with a full combo. They often don't see it coming and get hit by both the Q and E, then are forced to tank two plants for as long as they're snared. Try to avoid Athene's and other heavy mana items. Her early game is difficult to manage her mana, but her mana scaling is good enough that mid to late game you can spam comfortably with just a morellos. Keep in mind that her Q plant has range, but her E plant has slows. It's often good to do one of each, but two E plants is usually not a good idea. Two Q plants is okay, but not two E plants. When using your ult, even plants you spawn after the initial cast will be buffed. When using your ult, it's often a good idea to fight inside of it, even if that means dying. The knock up leads to an easy passive, and the buffed plants combined with your passive will nearly always be enough to kill. Last but not least, if you know you're going to die, try to land a double planted snare right before you do. The snare combined with slowing plants leads to a near unmissable passive.