While painting, avoid loading the brush all the way to the ferrule as dry paint getting clogged around the base of the hairs will tend to push them apart and stop them from forming a point.
Always wash your brushes with cold water as warm water will make the ferrule expand, loosening its grip on the hairs. After use, wash them in cold running water and either soap, washing-up liquid or brush soap by swirling the brush in your hand and then rinsing and repeating until no more colour comes out. Brush soap is best as it will also remove any dried paint and most staining.
You can also use hair conditioner or a brush preserver to protect your brushes. This is especially important if you use enamels.
Hold the brush and flick it in the air, being careful not to hit anything with it, to remove excess water and return it to a point (I do this by passing the hairs between my lips but its not the best habit).
Store them in a case to avoid direct sunlight and try to keep the plastic caps which came with the brushes to protect the hairs. Make sure you repoint your brushes before placing the caps onto the end to prevent bending stray hairs.