Focus on basic construction before all else:
Learn to study the instructions from the parts diagram through every step BEFORE you do anything else on the build. Learn to recognize and anticipate construction problems and how to visualize the way the parts should fit together. Understand that you might have to look at several views of the parts in multiple steps to really know how those same parts are supposed to go together.
Learn how to remove parts from the sprue without breaking them and how to remove sprue attachment points without leaving divots or bumps.
Clean up the entire molding seam all the way around the part. There is ALWAYS at least one, 360* mold seam running around every part. With slide-molded parts, there are additional 360* mold seams that intersect.
Learn to spot parts that have mold drift tapers and how to tool them into regular geometric shape (proper squares, cylinders, etc.). Learn to use a sanding block to square and smooth gluing surfaces and to true-up edges (and to remove drift tapers).
Learn to ALWAYS TEST FIT parts together before you cement them. Be patient enough to re-tool the parts if they don’t fit perfectly when test-fitted.
Learn to cement parts together without glue smears or squeeze out. Learn how much cement to use in different situations - small parts, long seams, etc. Learn how to deliberately use glue squeeze out to your advantage to fill seams.
Learn to cement parts together properly aligned - “plumb, level and square.” Learn to close one eye and view assembled parts from at least two directions at 90* apart to estimate how square they are to one another. Learn to view down assemblies with many parts that are supposed to be in alignment, again, by closing one eye. Closing one eye mitigates parallax distortion by “disabling” your binocular vision.
Learn how to clamp, tape, rubber band, and use other fixture methods to hold parts in proper alignment. Learn to be patient and allow for glue to dry / set as long as is necessary.
Learn to think in sub-assemblies and to plan ahead and anticipate the way you will want to paint, finish and do final assembly. Learn how to plan out the entire build, to include the finish before you ever start the construction.
Learn what general steps that you can skip ahead to that make the build process more efficient, like cleaning up a few suspension parts every build session as you do other areas so that when you get to the steps where you may have literally dozens, if not hundreds, of individual parts, those parts are already to go. This also mitigates “build fatigue” so that you don’t have to spend hours doing the same repetitive task by spending a few minutes every session (maybe as a warm up or final bit on mental "auto pilot at the end).
Learn to anticipate and how to “build around” potential construction sequence issues. Many times kit instructions show a construction sequence that is easiest for the person who draws the illustrations rather than for the person who is actually going to build the kit. Usually - but certainly not always - it’s better to construct major components from large parts before adding the details which might be vulnerable to damage as those subassemblies are handled. Learn to visualize this so that you will know when to deviate from the instructions and when you have to follow them to the letter.
Excellent models ALWAYS start with excellent basic construction. There is no such thing as “advanced” skills, only ever more polished and experienced application of the fundamental skills. Advanced modelers are not “advanced” because they have some secret stash of techniques known only to them. They are “advanced” because they don’t accept anything less than perfect execution of the same basic techniques that all modelers use.
There are analogous basic finishing techniques, but before you worry about those, learn to prioritize good construction. Models with the most beautiful finishes that exhibit basic construction flaws will always be substandard and can never really be considered “excellent.”
Finally, the most important lesson for any beginning modeler is that the ONLY thing that matters in the end is, “Are you happy with the results?” The only person you ever have to satisfy with your modeling is you.