Buy a good-quality brush or roller. A cheap brush loses bristles, doesn't hold as much paint, and is harder to use when "cutting in" to another surface. Cheap rollers tend to mat and leave an uneven stipple on the surface.
Paintbrushes are designed for particular functions and so come in a variety of shapes. The angular brush is used to trace fine lines and cut clean even edges. The straight brush is used when precision is not required - for example, when painting large surfaces after cutting in is completed. The round paintbrush is useful for curved surfaces such as mouldings, railings or pipes.
An extension pole on your roller handle allows you to use longer strokes and saves you from bending over to refill the roller with more paint. It also speeds up the job and makes it easier to maintain a wet edge - especially important on ceilings.
Drag and drop your favourite to create your own unique CIL color palette