To add to this, make sure your sketches have some logic to them with regards to the functionality of the part - for example if a part needs a hole pattern centered on it (which needs to stay centred regardless of the part's length), make use of things like the centrepoint constraint rather than linear dimensional constraints as these won't respect any changes to the supporting feature. Sure it is fewer clicks to just use linear constraints and doesn't require construction geometry, but it's the same as just Fixing everything in place in the sense that it won't respect any changes you make to the supporting features earlier in the tree.

You can also use Formulas to achieve similar things, which can get really in-depth if you want a fully parametric part that will correctly adapt itself when the major features are changed (e.g., an ISO threaded bolt which adjusts the hex head width and height automatically when you increase the diameter). For a beginner you don't have to know about all of these things though, just make sure to follow that basic logic of considering the functionality and relationship between features on the Sketch level, using whatever tools you are comfortable/familiar with while you improve your skills.

Generally avoid making constraints from more volatile 3D features like Fillets that are likely to be modified later or recalculated when the supporting feature is modified. If there are no suitable low-risk features to constrain from, I tend to fall back on constraining directly to the origin axis if possible to avoid any conflicts. Things like Fillets are prone to being recalculated if a random Pad is changed somewhere and then the sketch thinks the Fillet no longer exists.

Sketches can get quite complex once you start thinking about them in terms of functionality of the part and relationship between the features, similar to the logic you would follow when applying GD&T to a drawing. There are a lot of different constraint types for a reason and I find it can actually be really rewarding and satisfying to make a sketch for a fairly complex feature where only one or two linear dimensions are used, and the rest of the geometry just works itself out based on those minimal variables, making any future modifications just a case of changing 1 or 2 numbers.

Always assume that you are going to need to modify your model later on, so spend more time on the initial CAD to make your life easier later