Some good tips here already. I wouldn't choose a fad diet like Atkins or whatever else is out there-too many rules and most people don't follow them forever. Adding all the fruits and vegetable someone else mentioned is great, and eating a big salad before dinner-love that suggestion. Number one is noting all the food you eat, every little bit. I was shocked at how much I ate once I kept track, and knowing I have to write it down actually stops me from consuming more. The hard part is being honest in that because it can be easy to "forget" to write down that last cupcake before bed.
I think walking 30-60 minutes a day is a fabulous start. I'd just keep with that and as the pounds come off, you can increase your intensity and possibly start jogging. A bit of weight training or calisthenics would be good to add eventually too. You don't even have to join a gym, many exercises can be done at home using your body weight. Do some google searches and you'll find something you like! Good luck!