I had baby #2 and gave myself to her first birthday to get to my desired weight. I was able to start when she was 7 months - here's what I did. I was successful to getting to my pre-pregnancy weight by the baby's first birthday. That was phase I. Phase II is to better my BMI rating (about another 10 pounds to lose). This was all baby steps - not all at once.
#1 - stopped overeating. My big down fall. This was in about June.
#2 - started getting my 4 servings of veggies every day (this was my downfall - fruits were easy, veggies were tougher). Eat a big salad nearly ever day with a mere 2 Tbl dressing, and lost of veggies.
#3 - Set a realistic expectation - 20 pounds to lose in the first year.
#4 - Exercised following the No Excuses Weight program (Jonathan Roche - via Fly Lady). Interval exercises 3 times per week, 2 or 3 strength training. I started with 10 minute sessions, and have increased to 30 minutes. I use videos for the cardio. When the weather is better, I'll get back outside and push the kids in the stroller or walk the dogs. (Jonathan says 1 - 2 pounds per week is realistic). You can google him. Inspirational, that there are no excuses to working out - I can find 10 minutes if needed. My library has exercises videos - they have a series that are 5 workouts, 10 minutes each. They are awesome. You can mix and match the workouts in each video for a routine.
#5 - it's as lifestyle change - this is permanent. Eating veggies, not overeating, being a good role model for my kids. Read the Julian Michaels book, and have made some changes to organics where we can. I eat 5 times a day: Breakfast - mid morning snack, lunch, afternoon snack, dinner. No eating after dinner - just water. My mindset is that it's about what my body needs, not about what I want.
#6 - my thyroid was hypothyroid - diagnosed after baby #1. I keep my scheduled appointments and keep this in check.
Best of luck, start with one thing, master that, then go on to the next thing. The bottom line is to consume fewer calories than you exert. www.mypyramid.gov has some great tools. I charted what I ate for one day and was SHOCKED at how many calories I had consumed - even with healthy food.