I'm sorry about your marriage.
FIRST you need to give yourself some time to get past the last relationship, even if this divorce is a "good" thing.
I tried the personals for a bit when my marriage went tits up. A lot of it will depend on what you are looking for. If you just want to "hook up" you will have pretty good luck with Yahoo, AFF, and the like. If you want a relationship, you are better off with sites like Match.com or e.harmony. You pay more, but people there are generally more serious about what they are looking for.
Write a good profile/ad. The more you write about who you are and what you are looking for, the better your chances of attracting a match. Include a picture. Face it, there are a LOT more men than women on these sites, and women may get hit by 20 or 30 or more contacts a day. You want to stand out in the crowd, so make your profile special. And for the love of God, PLEASE proofread for spelling and grammar!
Also, we (women) have a tendency to think that if you don't care enough to write a complete profile, then you probably are not too serious about looking for more than a fling in the hay. Profiles that say, "I'm no good at this, so you'll have to get to know me when we meet" will not get you many dates.
If there are things that are important to you that are non-negotiable, such as firearms, smoker/non smoker, religion, kids, etc., include that in your profile. Don't waste your time or hers by leaving out that kind of information.
BE HONEST. I once had a date with a guy who described himself as 5'11", athletic build, with a full head of hair. He was, in fact, closer to 5'4", his "full head of hair" was a particularly pathetic 6-strand comb-over, and the closest he came to an "athletic" build was that he was shaped like a ball. Another guy had pics... from 10 years ago. If you lie about something so obvious as your appearance, we won't give you a chance to lie about anything else.
Once your profile is complete, don't just sit back and wait for the chickies to run to you. Be aggressive. Spend some time going through profiles, and contact everyone who looks promising. Write a little more than, "Hey, write back if you want to hook up." Tell the woman WHAT in HER PROFILE attracted you, WHY you think you two may be compatible. It takes a little more time that way, but those personal details will separate your e-mail fro the rest. NEVER, EVER make any sexual reference in an introductory e-mail! And again, USE SPELL CHECK! Poorly written e-mails leave a bad first impression that will probably not get a response.
Many of them won't respond, some will be polite no thank you's, but you'll get some bites. The more times you cast, the better your chances of reeling in a keeper.
And if a woman doesn't reply, don't take it personally. I know quite a few women who stopped sending "Thanks but no thanks" responses, because then men often would reply with really mean e-mails ("You think you're too f*ing good for me or something?") and they have decided that it was better not to initiate a dialogue with someone that wasn't a match. Not MY style, but I understand where they are coming from. Again, don't take it personally, just keep at it!
Good luck, and happy hunting!