If you are the adult in charge of helping the youth group organize its fundraiser, it's a great idea to get the kids involved from the start. Have a meeting where everyone can get together and discuss what needs to happen. You need to talk about what projects the group wants to fund, how much things are going to cost, and how they want to go about organizing some fundraisers for church youth groups that will help them reach their goals.
You might be surprised at all the great fundraising ideas the kids come up with on their own, and if you can just help them push things in the right direction, they'll actually do most of the work themselves. The other main factor in planning fundraisers is to select a fundraising activity that suits the group well. Set an afternoon aside and do a little research - have a look at some direct sale and pre sale fundraisers, and see what might go well with the goals you have set, the time limit you have, and the fundraising team you have at your disposal.
Smaller groups, for example, may want to stick to high profit ideas like scratch cards or pizza cards. Other fundraisers for church youth groups can range from catalog fundraisers, to candy bar fundraisers or even tea and coffee. The sky is the limit - you just have to look at all your options and select the one that matches your situation.