in bars and massages you need to have great looking wallet , don't worry too much about body.
But smile a lot and pick up boy who will smile or at least look back at you.
Rest will be easy , we all were nervous on the first time there and now we don't even remember why.
Don't think too much , just pack your suitcase and go , you are in revelation of how paradise looks like.
Since you are young you may score plenty of free in clubs like DJ Station, Silom soi 2
JUST DO IT AND GO !