It can be baptism of fire for first timers! Be warned, the internet dating seems to be the marmite of MN, you will get some very polarised views ranging from happy 'I met my soulmate' through to 'everyman who uses OD is a cheating, lying bastard', I imagine the truth is somewhere inbetween.
A few thoughts of my own:
Not sure what site you are using but its probably worth forking out and becoming a member of an established dating site, free ones tend to be populated with skinflints, weirdos and Nigerian scam artists.
While you are trying to 'sell' yourself in the best possible light dont embelish things too much, playing tennis on holiday a couple of years ago is not a hobby! If you describe yourself as 'athletic' make sure you are!
Dont spend forever exchanging emails, swiftly move to chatting on msn/skype then a chat on the phone if you are comfortable (withold number), you will find out volumes more about a prospective date as emails dont always convey personality, humour etc.
Set up an email address spefically for the use of dating
Honesty is the best policy, if you dont fancy someone after a date a polite 'had a nice time but I dont want to take things further' would be appreciated rather then just a rude radio silence
Always stick a photo(s) on your profile, preferably recent.
Your gut feeling is usually the right one.
It might take a few dates/weeks for your 'radar' to get up to speed and you will soon be able to more easily weed out the timewasters/idiots and spot red flags with greater confidence.
Arrange first dates as a lunch or simple drinks after work, you dont want to have a 3 course meal only to find the chap is a complete bore and you have no easy escape.
Always tell a mate where you are going when meeting someone for a date.
Dont play mind games, if you like someone tell them, if someone you like asks you out on a second/third date, just get on and organise it, no 'make them wait' bollocks as they will just move on.
Actually have fun, it is not the be all and end all solution to dating, it is just another iron in the fire. Dont beat yourself up if a date does not work out or someone you took a shine to does not return to compliment.