Aim for Independence
Grade-school kids will usually require at least some assistance. But before you decide how much help to offer, check with your child's teacher. Most prefer that kids work mainly on their own so that homework can be used as a gauge of progress. That means restraining yourself from correcting your child's spelling or figuring out the math problem for him.
On the other hand, reading his work over and challenging him to find the three misspelled words you discovered is a good way to get him into the habit of checking over his stuff.
It's also never too early to teach the value of research: Demonstrate how to find answers in reference books like dictionaries, online, and in atlases. Or look for real-world solutions. The more you foster the idea of homework as a time for independent exploration, the more kids are going to enjoy learning.