I think a child's interest in learning depends on his/her environment. It is typical for children to mimic the activities that they are seeing; hence, when people around them are engaged in any learning activity, then that makes them want to learn things, too. Showing support also makes a huge difference. Parents should be hands-on in dealing with their child's needs no matter how small or big they are. I think there is nothing more enjoyable for a child than having to study about stuff along with his/her parents. Think of it as a way of creating a close relationship between you and your child.
Moreover, rewards mechanism may also play a key role with regard to improving your child's study habits. Oftentimes, when they have something to look forward to, they get motivated and strive hard to get rewarded. However, this trick can also be crucial, as kids may then lose interest if there weren't rewards being offered to them.
Although, doing these things do not guarantee that a child will be able to keep a good track record of study habits; hence, I still think that one of the best ways to address this matter is to observe them, and listen to them; ask them about the problems that they often encounter while studying so you'll know how you can help them.