I used to overlook tree dwelling birds, but I've managed to get a lot of good shots of my local sparrow, mockingbird or bushtit by following a few simple rules.
- Don't try to catch them in flight (if you actually have caught one of these in flight, I'm damned impressed, but for me it's not worth the effort).
- Get them perched in a tree or other structure. Don't bother shooting them on the ground. You'll want a nice background.
- Shoot at or near your lens' sweet spot, to get the sharpest picture possible. You'll want to get the texture in those feathers.
- Get them facing into the light. Bad for portraits but great for birding. If the light's a little off to the side, you'll get some depth to the feathers. Also take a few shots to get the head posed such that the sun glints off one of the bird's eyes.
- Get as clear a background as you can. Bokeh really makes the bird "pop".
- Try to shoot in the golden hours when the bird will be lit more from the side than overhead.
- Extra credit if you can catch the bird eating.
That's about it. Just remember, different birds photograph differently.