I was visiting with New Orleans Artist, Billy Solitario, one day and was asking him about adding people to my beach paintings - he does such a great job with that (and many other things!).  He told me to make sure my painting is dry and then with a lot of turp, just block the people in.  Make sure anatomy is correct and if not, you just wipe it off and try again.   It was so easy.  So today I tried it. Here's a video of my effort!  Hope you enjoy and learn something!  If you have a quick tip, share it please!