Are you in London? Things will be easier if you are.
Find a copy of the local free gay magazine(s) - in London, that means things like Boyz and QX, both of which are available online. Have a look at the club listings to see what sort of themed nights there are - apart from 'suits', how many of those types could you do? Are you fit enough to do 'sports wear' without looking as out of place as a Brazilian defender, for example?
Have a look at their escort section. The last time I looked, QX allowed more explicit ads than Boyz, but amongst the muscle, twink, leather and scally (all gay fetish types) ads should be at least one 'posh straight guy'. Consider making it one more - this can involve body shots of you in a good suit, for example, rather than 'here's my erection'.
When thinking of what to say, it is going to help to have thought about what your boundaries are: what are you prepared to do for the money? It certainly need not involve you being on the receiving end of anal sex, for example, but are you going to be ok giving? If you won't do either, put emphasis on what you will do - let clients suck you off / whatever. Are you ok with clients using drugs while with you?
Depending on just what markets you are going for, some of the other free press can make sense, but again it depends on where you are.