Well done for taking the decision to restart.
1) Buy a countdown. You will save money and as you have paid for 6/12 weeks in advance, will be more inclined to stick to coming to group and stick to the plan. Several members of the group I attend swear by this to keep them motivated.
2) Think about where you realistically want to get to, and then break down that point to more achievable goals. Give yourself affordable non-food treats when you reach each goal. Alternatively, put whatever you can afford per lb each week into a jar, knowing that when you reach your goal weight you will have a fund to kit yourself out with some new clothes.
3) Try not to think of this as a "diet". Being "on a diet" is a fast track to being "off a diet". The key to keeping weight off is not losing it in the first place, it is making small changes to the way you eat in order to improve your overall health and well being. The weight loss will follow as a matter of course while you enjoy healthy and filling food.
4) Use this site as a source of midweek support. Its invaluable. Every one of us is at a different stage of the process, and there will always be someone who has been there who can help and support you.
5) Keep a food diary handy at all times and fill it in! Having to write down everything you eat is a pain in the butt, but it is very valuable in terms of keeping you on track. It makes you much more aware of what you put in your mouth and makes you question whether you actually need to eat the thing you are eating or whether you are eating it out of habit or boredom.
That'll do for starters! Good luck!