Faster aircraft often overtake slower on the same routing. This is usually accomplished by flying at higher or lower altitudes. This is called vertical separation.
In Infinite Flight you should always be maintaining 1000ft of vertical separation at all times. At cruise you should look to have 5nm or more of horizontal separation. You can check your distance from the aircraft around you on their data tag above their aircraft, use this as a guide.
Reference: 10.3 of the ATC Manual