Anyone to do with matchmaking will have an idea about the things that will probably be seen negatively by a potential partner. The following paragraphs were written with matchmaking for men mainly in mind - as they still tend to be the ones to initiate contact - but most of it still holds good in reverse!
Please do not ask for a photograph in the first message. Far better to wait for your match to suggest swapping pictures before you meet so that you can recognise each other. All quality personals services recommend that you do not push to find out to much personal information too soon. If a woman wants you to know something she'll tell you - or make it pretty clear that it's OK to ask her.
Register free with Pearmatch.co.uk matchmaking.
Don't talk about anything of a sexual nature! No-one wants to know about your past exploits in a first message and it's highly likely that you'll end any chance of a relationship there and then. Remember, if you're are offensive to others then most matchmaking sites reserve the right to remove you from their service.
Be positive! Most people want to feel good about life and themselves, and much prefer spending time with people that share a positive outlook. Due to the nature of computers, many personals sites can seem a bit clinical and so it's the messages that tend to show the personality. Therefore, don't fill your message with a series of questions as if you're interviewing someone for a job. You want to show that you're a well rounded individual by talking about some of the things you like to do and by showing interest in the person you are writing to.
At the end of the day it's down to you to make the judgement call as to when is the right time to ask certain questions. Just don't be too pushy in your eagerness to get to know someone. On the other hand don't let things drift for too long either. Politeness can sometimes be misinterpreted as a lack of interest! Probably the best thing to do is to try to 'put yourself in their shoes' and think about how you would react to the questions you're thinking of asking. If you then think that you wouldn't react well to being asked a particular question then don't ask it!
Next - I want to be meeting single girls but how many messages should I send at one time?