WWI aircraft are good starting projects because they are pretty simple and don’t have complex curves. I think the best thing to start with are good plans and lots of reference materials. Try to find plans that include airfoil cross sections. That will make the wings much easier to make.
I’ve done a couple WWI aircraft. If you’re interested you can check out the WIP threads.
I also have a couple of YouTube tutorials that might be helpful. (There are obviously lots of great tutorials by other people too, so definitely take time searching for them.)
Another idea is to download a model somebody else made and study how they made it. Blend Swap has some decent WWI aircraft. You could download some of them to see how they were made.