If you are driving stick and don't put it into 1st or 2nd before you try to hit reverse you were not taught properly. The reason this is important is that reverse doesn't have synchro gears so if anything in the trans is moving then it will make it hard to get into reverse.
Also, this could indicate a minor clutch release issue. Try adjusting the clutch. Drive the car before and after you adjust it to be sure if it really did anything. Turn the car off, put it in first. Pedal down to the floor then release. Put your foot under the pedal and pull it towards to. Pedal down to the floor again. Repeat that like 2 or 3 more times.
Also, this could indicate a minor clutch release issue. Try adjusting the clutch. Drive the car before and after you adjust it to be sure if it really did anything. Turn the car off, put it in first. Pedal down to the floor then release. Put your foot under the pedal and pull it towards to. Pedal down to the floor again. Repeat that like 2 or 3 more times.

lol