I think the main difficulty is with the rig that comes with the model(s). If it is simple, but flexible, it can be easy.
As for the learning part, you can try something I did to accelerate learning 3D animation from scratch (not sure how well it'll work with 2D):
1. Open file with model
2. Animate simple action
3. Render result
4. Delete all keyframes
5. Repeat steps 1-4 about 3-to-5 times
For the action, pick something general like a wave or a punch or picking up an object. When you animate it a second/third/etc. time the idea is to do that general action again, not repeat exactly what you did before (so, the wave or punch can be a slightly different one or done in a different way). The point of rendering is obviously to have evidence to compare for later, but you delete the keyframes so you won't be tempted to copy what you did before or use them as "reference" (you don't need them, trust me).
Doing it 3 times is about enough to get comfortable with whatever it is your practicing, but after 5 will start getting repetitive and you won't get much out of it.
You can also use this same method to practice stringing actions together to make a sequence and figure out your ideal workflow (as well as try out alternative approaches).
This should be the fastest way to practice and get good.
Good luck to you.