Small efforts every day (always have one rest day in a week though) is better than 1 or 2 big rides a week. Specially when you are starting out. This will improve your endurance quite quickly but without killing yourself trying to do a massive ride each week.

Gradually increase distance so you don't put your body under to much stress.

Make sure your bike is set up properly in terms of saddle height, bar height, stem length etc. It will make it more comfortable and encourage you to ride. Aching back and knees etc is never going to be a good thing.

The biggest tip though is to enjoy it. You'll want to go out and it won't feel like going to do exercise for exercises sake, it will be just something you like doing.

Hey time4changexx I started riding because walking at the park and the eliptical machine are boring. I bought a used Univega Via Montega in June of last year...Before 2012 was over I had purchased a 2013 Fuji Absolute 1.4. A nicer hybrid/ fitness bike with an aluminum frame and carbon forks, blah blah blah..frankly the Univega was good enough for a guy trying to lose weight, but I wanted to get something that looked more modern.
I try to ride afterwork sometimes, but i live in Los Angeles, and the dedicated bike paths I like are along paved rivers, so the bike paths are really windy in the afternoon.
My advice would be to only do it as much as you enjoy. I've pushed myself too hard and ended up with cramps and what not. i would have liked to see myself riding 100 miles this year...I can do about 50 in one session, but after that my arms and legs go numb, and I start cramping regardless of how much gatorade i drink.

I think the biggest thing for me is realizing I'm not in the Tour de France...I'm just a dude trying to be more fit...i don't need colorful $100 biking jerseys or the latest bike with clip on bike pedals or what not...

Cycling's a great way to burn some extra calories, it's non-impact (providing you don't fall off of course), and the passing scenery provides enough interest to keep you exercising far longer than most other exercises.

I returned to riding just over 2 years ago, after a long lay-off due to work etc. When I began I was just short of 400lb (397.7lb for the sake of accuracy, or 180.4kg in sensible measurements!). By following the guidelines on MFP I've dropped to 105.4kg in under 2 years.

When I began riding again, my regular riding loop was just under 16km (10 miles) and took me just over 1 hour. For the following hour, I was pretty much unable to do anything more than sit wheezing and gasping before dragging my sorry carcase upstairs for a shower, and a short nap. My typical riding schedule at the moment is 3 days riding with a rest day. Normal daily rides are generally a 50km (30 mile) loop in 115-125 minutes with maybe 6 times the ascent/descent that the initial loop contained. So - I'm going 3 times as far on twice as hilly terrain and going 50% faster... that's quite an improvement in riding ability - it's not spectacular by the standards of "proper" cyclists, but it's an improvement that I attribute mainly to losing the weight - 75kg is not to be sneezed at...

Best of all, I can cheerfully go out on a Sunday morning, ride for 70-80 miles in 5 hours, arrive home, and still be perfectly functional after a shower and a bowl of pasta

Oh - and advice... well, if I had to give one single piece of advice it would be this...

"Find A Good Local Bike Shop" (LBS)

- a good LBS will make sure you're riding the right bike for the type of rides you're doing, they should be able to ensure that the bike fit's properly (not JUST a matter of how high the seat is, but the reach to the bars, the drop from saddle to bars, bar width, type of pedals/cleats crank length and a dozen or more little tweaks that mean the bike fits like an extension of your own body, not just a sack of scrap metal and rubber under your *kitten*!

+1 - Also be aware, cycling can become quite obsessive!

Do your wrist bend when you are riding? Keeping the wrist strait will help with the tingling. You may want to check your LPS, you can get grips to help with that. Kinda like this but a bit more nicer.

http://www.hardwareonlinestore.com/index.php?option=com_virtuemart&view=productdetails&virtuemart_product_id=79664&virtuemart_category_id=3106&Itemid=1&gclid=CObC7ovnibcCFeU-MgoddFQAgw

Wow you just started riding 3 weeks ago and your doing 8-12 miles in an hour. I started April 4 and I can barely do 3 miles in 45 minutes. You must have lost all your weight and be in excellent health to be biking that many miles in an hour. I can't see myself doing that many miles until maybe the end of the year.
The one thing that really bugs me with the biking is my hands start to tingling and really hurt. I have CTS anyhow but when I am on my trike ( balance issues can't ride a bike yet) I go into a full blown spasm in like 10 minutes. Of course this makes the next 35 minutes very uncomfortable, but since I think I have become addicted to triking I just keep pushing onward.
Good luck to you, I am sure you will make great strides in your biking endeavors.