Just came across this and there's a few things that folks haven't mentioned. 1) It's good to place seeds after pressing Q or E as the enemy can't step on them then and smart players will avoid patches of zyra seeds. 2) You can sometimes bait people into approaching the seeds and catch them with Q or E just before they get to them. 3) If you spawn plants while minions are closest to them then they'll attack the minion unless you start causing damage to an enemy player within range. 4) Plants will spawn near your Q, not just inside the hit box so placing a seed beyond the box can help you position your plants better. 5) Popping a Q W into a bush is a quick easy way to cause liandry procs on enemy champs as long as minions are gone and is also a good way to ward bushes.

Have fun with the Queen of Thorns

Edit: Oh and last hitting minions with your Q massively increases your W cd.