First I try to read the room if I am joining a scene in progress Are people RPing actively? Perhaps it isn't the time then to run in and flip tables or be disruptive in the scene bc I think it seems a little boring.
Second, I try to play off what other folks there are doing in a way that doesn't mean they have to go out of their way to interact with me. Paying attention to other people's poses seems to be a shock to many people and I tend to get positive results from it.
Third, making sure I have realistic expectations ooc. If I'm having a down day or feeling strongly like no one will like my RP or I would be super disappointed if nothing clicked then for me personally that is a day usually when I will /not/ go out to trawl for random RP. If I am super grumpy and am going to be very annoyed at grammatical errors or people not always reading my poses thoroughly (and I'm not in the mood to find the humor in it) then that also probably isn't a great day to go rando just because I am not in a space to enjoy things and people in a less controlled/known environment and that's not really fair to anyone and is setting me up to feel aggravated.
If there's no scenes in progress and I am soliciting for new RP then I try to have a couple of scenarios and places to suggest specifically to folks on the seeking RP channel or when/if they respond to a page. That way I can pick stuff I enjoy! If it is a blue moon and the other person has ideas at the ready that is honestly so rare that it is a treat!
And importantly to either type of social rp, I always have an exit plan oocly. How long I will stay to give things a chance to spark. How I will jump out or hopefully end something in a graceful and positive way once things have run their course.
I find ending scenes gracefully to be the hardest and something I'm working on.
But honestly, the single best predictor of being able to have fun and enjoy scenes for me personally is being sure to manage my expectations, make sure that I'm in a good place to /be/ a good RP partner, and to try to have a list of ideas/things I can springboard off of that are interesting and fun for me to play as well as things that can be incorporated into existing scenes without being overly disruptive (though sometimes people will give the go ahead to shake things up, which can be fun too, I've learned to be careful about doing that as an introduction.)