Find a cadence that works best for you. If you are fairly new to riding maintaining a cadence of 90 rpms probably is not reasonable. I would suggest first focusing on simply learning what your workable cadence is and what it feels like. If your bike computer provides this information that is a huge plus. Focus on maintaining this cadence for with time you will find it will increase as will your speed. Remember too, the cadence you settle into on flats is going to be different from the cadence you settle into when climbing but regardless of the topography of that area adjusting and maintaining a workable cadence is important. Hopes this helps.