Click a month of Ted's bonsai work calendar
The three things every bonsai needs:
1) Water every day.
If it's an outdoor bonsai and it rained that counts. If it's an outdoor bonsai in the winter with mulch; it might count. When in doubt water them. (Your soil should be set up to drain well and it will protect from root rot.)
2) The right amount of light.
Different varieties require different amounts of light. You should also rotate your bonsai weekly to balance the light it gets per side.
3) No critters.
Watch for spider mites, powdery mildew and caterpillars. Treat as found.
Spider Mite test
Place a white piece of printer paper under a tree branch and tap it. If you see tiny (get your glasses) spots moving around on the paper after the tap; get the miticide.