Set a schedule. While this can be flexible, it's a good idea to have a set time when students do their homework. Many students need a little time to unwind after school before tackling their homework, but doing it too close to bed time may be difficult due to fatigue. Find what works best for your child.
Provide a home study center for your child with adequate light and few distractions. Doing homework in front of the television is typically not a good idea. A dictionary, paper, pens, etc., should also be readily available.
Be available when your child is doing homework, so that you can answer questions if there is confusion. If possible, it is better for you to be in another room, so you are easily accessible and yet not a distraction.
Don't do the homework for your child. While help is encouraged, I don't expect perfect work all the time. Seeing the pattern of errors is often helpful to me.
Check homework for completion. While students should be responsible to complete their own assignments, you looking over what they've done a) keeps you informed of what your child is studying, b) provides the sometimes necessary reminder to complete the work, and c) shows that you care about what your child is working on.
Praise your child for his or her diligent work, as well as for accomplishment.