One of the best things to do on Tangiers beach is watch the games of fast-paced football the local kids play or the incredible gymnastics the beach athletes perform, sometimes for tips, but mostly for fun. You can even join in if you want. Playing in your bare feet is very different though!
You can also chill out in a beach bar looking out over the incredible views to Spain and the massive ships crossing the Gibraltar Straits.
Although you do get a few dodgy sorts on the beach, they mostly come out at night and now that the beach is lit up and patrolled by police this isn't really much of a problem.
It's best not to change on the beach. This can be seen as crude. Use one of the cabins belonging to the beach bars.