Climb below your max grade, especially when you start. Placing your own gear and learning to be confident with it will take some time, don't stress it out with difficult climbs.
I like to talk with my partner about my gear placement right when he arrive at the anchor. So he can tell me how gear felt to him after I climbed (eg, if the red one popped out because I didn't place it well).
If you want a rest, tether yourself to the last gear rather than resting in the rope. It puts less effort on the gear.
Similarly, always lay down in your anchors so everything is tight. You don't want slack between you and the gear because the shock of a fall has higher chance to pop it out.
A tree alone is fine to use as an anchor if it's larger than your leg.
Always take a headlight.
Don't learn any of these the hard way ^^