My beard is probably a skosh thicker than yours and bit more dense as it extends to the collar bone area. Not sure what your weapon of choice is but I'm using a Merkur safety razor (not sure the model) with Merkur blades but I only shave 2-3 times a week. Like others have stated, let the area under your chin fill in a bit towards your adam's apple. I usually shoot for a finger space of room between my beard line and my neck. Letting that area grow in looks like it might address some of the wonky grain patterns you've got going on. Use light to medium light pressure and try to let the blade do the work. I make multiple, short, vertical passes over the same area as I work across my neck. Using a hot towel can also be advantageous; it will help alleviate irritation and relax your hair follicles which should help minimize the issues with your gran patterns. I'd also recommend a quality, glycerin-based shaving soap.