this is the first question that I post here, I want to know how the ambient occlusion bake works due to the work I did on these 2 models
(high poly is still wip) 
and this is the AO bake I managed to make

I'm a complete noob when it comes to creating textures through bake, how can I avoid all that problems and artifacts in bake? for example the grid in the center has completely black results whereas the middle plate of the grip has a good result




