I HATE brush-stroke marks. For painting furniture or cabinets-- add floetrol by sherwin williams to your paint when painting furniture or cabinets and it will take away all of those brush stroke marks and leave the paint smooth.
Use vinegar and hot water to clean your paintbrushes. Fill a small bowl with vinegar, hot tap water and soak for about 30 minutes. If you have a brush thats really dirty and has dried paint on it, put your brush in a small pot and cover the bristle