take it easy the first few rides, you have your whole life left to do it. but it's also normal that you have DOMS after not doing a lot of physical activities for some time.
- it's important that you setup your bike properly (seat height etc).
http://www.bikeradar.com/beginners/g...n-right-39738/ or
http://www.peterwhitecycles.com/fitting.htm are two (of many many) guides how to do it. most of them have some things in common and disagree on some things. you can also ask a local bike shop to fit you. if you have a decent shop nearby, that's probably the easiest option. it shouldn't cost too much, and if you bought your bike at a local bike shop, it is very often free.
- as i said, don't overdo it in the beginning. it's easy to get carried away. but your body needs time to adapt to these new requierements. i'd suggest to just ride 2-3 times a week for maybe an hour or an hour and a half. most of the time, you should ride at rather easy pace (so that you could still hold a conversation). of course, this depends on terrain.
- after a few weeks, start to incorporate longer rides once a week, maybe 2-3 hours, as mkay suggested. if you don't have friends that you can ride with: there are A LOT of local group rides that you can join. google should help you, or again, ask local bike shops. most group rides will probably be too fast for you (at least for the next few month), but over time, they will become easier.
- after that, do whatever feels right to you.
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http://forumserver.twoplustwo.com/85...s-lsd-1242248/ is a cycling log with some good discussion on differing topics, if you feel like reading a little bit.
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www.strava.com is very popular in cycling and a great way to measure your progress.