If you're starting from scratch, get a heart rate monitor and figure out your zones. Mostly keep your HR in zone 2 to begin with. Try to increase your weekly riding time 10% per week, indoors and outdoors combined. Try to perfect your pedaling. Everyone is different, but I find I can ride for up to 1.5 hours at a time on my rollers without going mad. It helps to listen to the international news so you get really p1ssed off. Takes your mind off the boredom. Buddhist meditation CDs are good, too. Well, music is OK, too.
If you can read, you're not concentrating on your pedaling enough.