It is a daunting prospect attending your first party, my knees were trembling as I made my way to their old Lancaster Gate venue for the first time 2 1/2 yrs ago, but I was made welcome, helped to find my way and after 5 mins with a nice girl my nerves settled and I haven't looked back since 38 parties later!
With the 2:1 max ratio there's always somewhere to join, the girls are pretty proactive in making room. As ipad3 says, it's likely that a free girl will be asking you to play, especially if the guy count is lower. Maybe try to go this week while the tube strikes are on. I've heard the 4-6pm is often less busy that the lunchtime & evening parties, if you can make it.
The new venue is a very smart, spacious, high-ceilinged apartment, wooden floors, 3 bedrooms, 3 bathrooms, a sitting room and large kitchen with refreshments available. The action takes place in the bedrooms where there are various beds, a love-swing and chairs. The doors are all open, so you can wander where you like and join in wherever. OWO is pretty universal, sex is always with condom which are provided, no anal, some girls allow kissing, RO and fingering but you have to play that by ear.