I would suggest that you forget everything you learned about CAD when starting out in Fusion. I would suggest you make your sketches as simple as possible. Aiming to fully define a sketch in Fusion is a futile task. Aim to do as much with 3d geometry as possible with things like Combine, fillet, chamfer etc. Realize that "documents" are not really assemblies as much as they are a ton of parts that can be positioned with joints. That means their position is captured with timeline features. Every few steps try to break your model so it stays robust throughout the entire process!
There are two camps with components; never work in them and let Fusion handle it, or always work in them explicitly and force Fusion to handle it. The first one is easy but sometimes you'll find yourself stuck trying to do something simple like move a component. The second one requires focus and will take away from the experience.
Eventually you'll figure out that you can crank out robust sub-assemblies really quickly without much hassle. Good luck!
Note: Learning Fusion has forced me to think a lot about how CAD systems work and as a result I have become a far more powerful user in other CAD packages. Kind of a nice perk of learning Fusion.
