So, for a plane like the 737 (or the 777) flying a fully configured plan in the FMC, you basically want to let the plane do its thing, especially since you’re still learning how to run it. Take off in VNAV, let the FMC in the aircraft work the A/T system to manage thrust in the climb and cruise, and then let VNAV manage the descent. Simply dial in your desired lower altitude prior to TOD and the plane will descend itself and manage kinetic energy. If you’re not flying with ATC, dial in your FAF altitude (e.g., the altitude you would expect to acquire the glideslope for an ILS) and let the plane do its thing. If you’re too high or fast, the FMC will give you a message that drag is required, in which case you simply extend the speedbrakes to manage the speed. VNAV will get you to diale-in descent altitude with very little work on your part.
If your arrival has a vector leg, you may need to change to level change or V/S briefly during those segments, but generally VNAV works - it’s there to reduce pilot workload and manage aircraft energy in a controlled, intelligent manner. Take advantage of it! 
