I highly recommend working out first thing. I can trick myself into doing more when I'm not properly awake
If I wait til later in the day I'll convince myself I can't do it for whatever reason.
Also, I have much more energy when I'm excercising regularly, the first few times really are the hardest, especially if you are running or lifting weights, you'll ache and not want to keep going, but lighter reps help with that! Honestly, breaks longer than a few days are bad for me, my energy drops and I start feeling depressed. Just make sure you are eating enough to compensate for the extra energy expended!
I hate cardio, I'm all for weight lifting. Heavy weights at lowish reps, easy!
http://startingstrength.wikia.com/wiki/Starting_Strength_Wiki
http://stronglifts.com/
Pick something that allows you to set goals, it's a huge boost when you reach them. I just started with heavy (for me) weights, now even when I go up 5lbs I feel awesome.