My tips:
If you've been in a controlling relationship (or even if not!) think of all the things you couldn't do when you were with your ex, and DO THEM! Make a list of the nice things about being single and look at it if you are feeling down about things.
If any of your children are under five, find your local surestart centre and use it - mine has been a fantastic source of support, one dodgy HV, but other than that, fab. Everything is free as well which really helps.
If you get any time where the DCs go to their Dad, use the time wisely. Sleep or read a nice book or get the house spotless or go to the cinema (on your own!) or something. Don't sit around on mumsnet or similar which you can do any time.
Agree with emergency savings/fund. Just your change from the week is enough if you haven't got much spare cash. Also, budget, but include in the budget a little bit of money for treats and/or just to spend on yourself.
Invite people round in the evenings - if you know any other single parents, invite them for dinner, then put the kids to bed all together like a big sleepover, or let them fall asleep in front of a DVD, and have a girlie night in. It breaks the week up a bit.
You NEED an emergency supply of wine/chocolate/cigarettes/anything else that gets you through. Because there will be really shit days. Don't feel guilty about it, as long as it's under control.
Tips for having a good relationship with your ex/dating/etc:
Never badmouth your ex in front of your kids. Grit your teeth, smile and tell them that he loves and cares for them very much, whatever the truth may be. They can (and trust me they will!) make up their minds about him when they are older. If you think he's likely to let them down it might be an idea not to tell them he is coming until the last minute (depending on age etc)
Don't stay emotionally involved with your ex - try not to get sucked in if he is spinning you a sob story. It's easiest if you have a third party you can communicate through in the early days but that isn't always possible. Try to keep communication to email or text so you have a record of what has been said. Be polite even if you want to shout abuse at him.
Don't use access to the children as a bargaining tool. Of course don't hesitate to stop contact if you think their safety is at risk, but if it's just him trying to get at you then don't bring them into it. Set an arrangement and stick to it as much as possible.
Take a break from dating for a while - when you do start dating, don't be looking for anything too serious too quickly.
Develop interests, hobbies, etc - anything - do something that makes you happy. It doesn't have to be expensive or involve courses that need childcare (although if you have the opportunity then this can be great too)
When you start dating make sure you keep these interests going and don't allow all your happiness to rest on another person. Do things for yourself that make you happy.