it is a good practice to cull fruit if you have too many developing, where the branches bend to the ground or break off. Remove a bunch of plums when they are small, leaving enough for your future use on the tree to fully ripen.

I like to make fruit jams by halving and pitting a big pot-full of whatever fruit you have (you plums, me loquats AND plums right now), then simmering them with a cup or two of water, covered but stirred often. When the fruit is soft, puree with a hand-blender or regular blender, sieve/strain it back into the same pan and add sugar to your taste (usually more than you imagine!), maybe some squeeze of meyer lemon and some grated rind, or something spicy like cinnamon if you like to flavor it, or just pure fruit, then simmer it down until thickened. Jar up into sterilized jars and can/process properly, or just put in the fridge to eat asap.

also -- using a shortbread/sugar cookie recipe to make tart crust is easy. just bake and then top with your favorite curd or jam or chocolate ganache, and top with sliced or halved fresh fruit (or even partially dehydrated with wet fruit) and a simple glaze. YUM! Plums on lemon curd with plum glaze is great!