Change forms often.
Only go into open form (offensive form) when you are going to use ground spikes, uproot, or spike wave, and you have the mana to do so. Once you've cast one or more of these spells, immediately go back to closed form.
Remember that in closed form you have increased regen and armor, and that you have instant access to the bramble shield ability, which will often save your life (it doesn't matter what build you're playing as QoT - you need bramble shield).
This may seem like common sense, but anytime you play QoT you should remember - stay in bulb form unless you're about to bust out some offensive abilities, then go right back. You should stay alive longer and require healing (and limping back to the crystal) less often if you adhere to this philosophy.
Also, another common sense thing, but might as well mention: The hotkey for change form is 4. You should have a finger poised over 4 almost all the time. Don't bother actually clicking on the icon. To be honest you should use hotkeys for as many things as possible if you want to get better, but at the very least use the 4 hotkey for switching between open and closed forms.
