Sounds like you're talking about your health and fitness.
I find that it all comes down to commitment. Start with small goals and really commit to achieving them.
Even if you decide to take a short walk everyday you need to stick to it. Go out even if it's dark and pissing rain, you'll feel better for it.
Start small and keep going. When you start seeing results these will (hopefully) motivate you to set and achieve your next goal.
Tell your friends and family what you are doing so they can help and encourage you when you need it.
Good luck.