The single highest-leverage habit in mechanics is drawing a full free-body diagram for every object in the system before writing an equation. Students who skip it save thirty seconds and lose four points.
For an object on an inclined plane, resolve gravity into components along and perpendicular to the incline. Along: mg sin θ. Perpendicular: mg cos θ. From these two, most inclined-plane problems reduce to F = ma along the incline.
For pulley problems with two connected masses, the constraint is that the acceleration magnitudes are equal (assuming inextensible rope and frictionless pulley). Write one Newton's second law equation for each mass. Solve the system.
Friction on the incline: static friction points up the slope when the object is about to slide down, and vice versa. Kinetic friction opposes actual motion. Get the direction right before writing the coefficient.
Sanity check: does your acceleration point in the physically sensible direction? If a heavier mass on one side of a pulley 'accelerates upward' in your answer, you have a sign error.