When using latex be sure that the temperature is above 50 degrees F. It is difficult for latex to form a film at lower temperatures. With solvent-borne paint, be sure the temperature is at least 5 degrees above the dew point. If it isn't, water may condense on the surface as it cools while the solvent evaporates, causing an uneven blushing effect.
Even if your paint was mixed at the store, stir it thoroughly before each use. If it sits for a while during painting, it is best to give it a quick stir periodically.
When using a paint pad, apply the paint with long, straight strokes, all in the same direction. Do not pull the pad back over the painted area. Also, be aware that paint pads have a tendency to leave lap marks if you do not feather the paint carefully where one stroke meets another.
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.
Most exterior paints will cover about 400 square feet per gallon for one coat. But adjust for waste factors like the type of surface and equipment used. If the surface is rough or porous, add 20% to the total gallons figured. If siding is narrow (4 to 5 in.), add 10%. If on a corrugated surface, add 33%. Also add on a 10% waste factor if using brushes or rollers, add 20% for airless paint sprayers, and add about 40% for air paint sprayers.
To save on expensive solvent, try this when cleaning up brushes. Find two cans with plastic lids, one can smaller and one larger. Pour the proper solvent in the smaller can to clean the brush. After cleaning, pour the used solvent into the larger can. The sediments will settle out in a day or two so you can reuse the clear solvent that will remain on top.
If you want to re-use a roller cover on several paintjobs, it is best to start with the lightest color, then work in gradually darker colors, following each job with a thorough cleansing of the cover.
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.
When painting, keep a damp rag handy to clean up as you go. It's much easier to clean paint that is still wet.
If you find bubbles or specks of some kind under new wallpaper, first cut an X pattern over the defect. If the problem is a speck, remove it with a tweezers or a utility knife. Then work seam adhesive into the cavity, squeeze out the excess, and seal the opening. For air bubbles you also can use a paste-injecting syringe found in paint and wallpaper departments.