To be certain you'll have touch up paint you will want to buy a gallon or so extra and be sure to have the salesperson write down the exact ingredients of the paint you choose. Luckily, there are machines available which can analyze a chip of paint but, there's that old saying about an ounce of prevention...it could save you from buying gallons later.
Always seal your paint container tightly between paint jobs. This will help prevent your paint from thickening or evaporating. To seal a can properly, clean excess paint from the rim with a brush and then gently tap the edges of the cover with a hammer.
Never store paint where it will be subjected to subfreezing cold or extreme heat (over 100 F/ 37.78 C). Although most paints are formulated to withstand several freeze-thaw cycles, these conditions can ruin coatings by causing then to solidify.
When painting with a roller, don't fill the tray more than one-third full. Also, load the entire roller with paint by rolling slowly down the tray and back, several times.
To prevent air from entering partially used paint cans, store them upside down after placing the top on firmly.
Always store paint in its original container, with the label intact. This will help you properly identify rise color and type of paint when you go to use it again. If key information is concealed by paint drippings, write down the brand, manufacturer’s code, color, gloss level and type of paint on a strip of masking tape and affix it to the side of the can before you put it away.
Paint walls from the top down. If you are using a roller, start by making a large "V" or "W" (3'x3'). Then fill in between the gaps, blending into your initial stokes. Always work from the unpainted into the painted area.