Thanks for your replies, and sorry for my delayed response.  The main problem with the "beaches" you were adding is that they were not loose sand, gravel, pebbles, stones or shells based on available imagery. Further, natural=beach is for areas along the coast where wave action has shaped the landscape.   While this also sometimes happens along large rivers or next to large inland bodies of water, it probably doesn't occur next to small ponds or streams unless someone (if someone has hauled in some sand for the purpose of creating a beach it might qualify too if it mimics what would be found along the sea coast).

We have been having a rash of map vandalism related to people creating fake beaches, so I would expect any new beaches added would be scrutinized.  Best to start with mapping other features.

There is no need, and it would be no help, to insert a link to the wiki page. 

Regarding advice, the best place to start mapping is near where you live.  Get out and observe the world first hand and map what you find. You can then cite "survey" as your source.

Happy mapping!