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 marks.
For an inclined plane, resolve gravity into components along and perpendicular to the incline: mg sin θ along, mg cos θ perpendicular. From these, most inclined-plane problems reduce to F = ma along the incline.
For two masses connected by a rope over a pulley, the constraint is that both acceleration magnitudes are equal (assuming inextensible rope and frictionless pulley). Write one Newton's-second-law equation for each mass.
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.