The sport of inline skating is a great one for helping to increase your leg strength and power.
Because of the low position you take while skating you are putting constant stress on your quad muscles, causing them to contract for longer periods of time thus helping to increase your endurance capabilities.
When training for inline skating it is a really good idea to include lunges and squats. This will not only help to build up the quad muscles but will also really target your hamstrings and glute muscles which will also be heavily used while inline skating.
Having a good cardiovascular base will also be important because as mentioned above in order to maintain muscular contractions for longer periods of time your body is going to have to learn how to deal with lactic acid build-up. Try and work up to performing 20-30 minutes of higher intensity cardio work. Do not go as intense as you would if you were performing sprints, but try and make it slightly more intense than a moderate paced cardio session. Aim to work at about 80-90% of your max heart rate if you are very well conditioned and closer to 50-60% of your max heart rate if you are not. This will put you right at the lactate threshold and improve your ability to handle lactate greatly. Having a higher lactate threshold is one of the most important markers of a good endurance athlete.
Finally when training for this sport you will want to make sure that you spend some time stretching out your hip flexors. Due to the position you take and the fact that you are constantly pushing off with your legs and bringing them back into towards you, there is a good chance your iliopsoas muscle (hip flexor) will be tight. If they are not stretched out it can lead to future back or hip pain.
So take the time to implement a good training and stretching program and you will find yourself able to go faster and for longer periods of time when you hit the pavement.