I agree with Waffles about cycling at a pace where you are not out of breath - thiis means you will be able to sustain this for a lot longer and go further. It might seem that it cant be true, but as you get fitter you will go faster for the same effort anyway, without having to ride so you get out of breath, so you really dont need to push it - that tends to be counterproductive because you get tired more quickly and then disheartened when you can't finish the route you had planned, or have to stop and rest! Have some fun planning loop routes and setting goals if you like. If you're comfortable with a certain time or distance on the bike, try just doing an extra 2-3 miles, or an extra 10 minutes, then after you've done the new time/distance a couple of times, try going another 2-3 miles further, or for about another 10 minutes extra... etc. Any hills will make the miles seem harder and take longer to ride, so don't be disheartened if it seems to be taking a while to get any further/faster if your route is at all hilly. Once you're out on the bike for over an hour you might want to take something to eat with you as well as a drink. At the two hour mark it's a really good idea anyway. Just a banana or two, or sandwhich would be fine. Good luck!
