I highly recommend starting with Mark Sisson's Primal Blueprint Workout Plan. It's really simple:

• Monday – Sprint
• Tuesday – Lift Heavy Things
• Wednesday – Move Slowly, Play or Rest
• Thursday – Sprint
• Friday – Move Slowly, Play or Rest
• Saturday – Lift Heavy Things
• Sunday – Move Slowly, Play or Rest

For sprinting: I recommend finding a grassy field and running about 25 to 50 yards as fast as you can. Then walk back. Repeat! Start with three and work your way up to ten.

For lifting heavy things: you might try joining a cross-fit gym (I hear they're good with newbies) or get a good set of hand-weights. Also you could look into body-weight exercises. I try to lift really hard (within reason but without taking a break) for ten to fifteen minutes. I do squats, push ups, pull ups, and other simple things.

For moving slowly: you could go for a walk, a hike or a jog. Whatever you feel like! Or just rest on this day! Recovery is an oft underrated part of physical improvement.

The schedule above suggests doing each type of activity twice a week; but if you'd like start slower, you could try doing each activity once per week! Best of luck!

I recommend "Body by Science" by McGuff.

His approach is based on very intense workouts, but only once a week or so. He says that working out too often is a common problem, and that it does more harm than good, because it doesn't allow the body enough time to fully recover.

You can find a good intro to his approach on YouTube.

In my opinion, stronglifts.com. In order:

1. Read the introduction, following links until you don't feel like it
2. Read the e-book, supplementing with the rest of the blog
3. Start mobility exercises. Hip mobility foremost, then thoracic mobility if needed.
4. Start lifting weights as outlined in the e-book, as soon as you are up to it. Start with the empty bar. If it is too heavy, it's probably a mobility issue. Just do bodyweight and work on the mobility.
5. Go to the forum and start a training log. You can also ask questions there

Lifting weights has helped my posture, back aches, strength, weight and endurance. Crossfit is also great, but I prefer stronglifts, as I hate to exercise in a group at a set time. Also I fear burnout, which I've heard some people get with Crossfit. Starting a weight lifting program would also be good preparation for Crossfit.

Crossfit.com Amazing, life changing, the best shape you will ever get in, period.

Another place you may want check out along with what was already recommended is

www.rosstraining.com

His books are excellent and information dense more than enough to get your body and brain started.