Well played!
Keep at it, 30 soon, then 50 then the sky's the limit.
The main issue you need to begin to work on is fuelling. As you're getting to the 30 mark you are needing to start to take on board fuel from the start. Energy drink, flapjack, banana or jelly babies, make sure that you start to eat en-route. With a good brekkie I can just manage 40 miles on water alone, but no further. Time to start finding-out what type of fuel works best.
Eat before you're Hungry, Drink before you're thirsty - little and often is the rule.
Keep it up!