Use light weight spackle.  Press into hole then lightly smooth either with finger or putty knife. Slightly over fill.  When dry, lightly sand with sanding sponge.  Large holes may need to be filled twice.  Wipe over patches lightly with a damp sponge.  This helps hide the patch without the use of primer.  This is only effective for small nail holes.

• Clean trim so tape can adhere.
• Choose right tape and size,
• Mask baseboard trim.  Preferable use 6" paper with 3M masking dispenser.
• Mask the rest of the trim with 1" tape.
• Mask window and door tops with the 6" paper, and window sills and shelves that cannot be removed.
• Mask any areas that might be exposed to paint spatter.

• Carefully remove light switch and outlet covers.
• Place drop clothes under masking paper on the baseboards.
• Strain paint.  Many paints need to be strained due to the build up of solids over time.  If they are not strained these solid will end up on the wall.  Not all paints require this.  If you are not sure strain the paint, because these chunks ruin a nice paint job.  Straining paint - a paint strainer can often be purchased from your paint suppliers.  I recommend the 5 gallon mesh strainer.  Place strainer around a 5 gallon bucket then pour paint in bucket.  Lift the strainer and let drain, then place into a bucket of water.  The paint is now ready for use.  The strainer can be cleaned and reused.

I recommend primer if there has been patching that is bigger then a nail hole, and if the texture of the wall has been interrupted.  Primer allows the wall to be the same absorbency so the final paint finish will be uniform.  How to blend patched areas:

• Make sure the patch is sanded even to the wall.
• Match texture.  Many textures are available in spray bottle form.  Hand textures are a bit more complicated, we can help .   Apply texture and allow to dry, sand if needed to blend to original texture. 
• Prime the wall floor to ceiling that the patch is on.  I prefer to prime the entire room for an absolute uniform look, this however is not necessary.

• Always start by cutting in with brush first. Paint along the trim, outlets, switches and the ceiling, one coat.
• Roll the walls in a sideways z pattern going back to fill in.  Roll as close to the trim as possible without touching it.  Move along the wall keeping a wet edge.  Go back to the starting point and roll straight down, overlapping each stroke 50% straight down only.  This is called laying off.  It is a painters secret to an even finish.  The paint must stay wet the entire time this is done.  Start again with the sideways z pattern repeating the entire process with the wet edge.
• After paint has dried, repeat the first two steps.
• Remove tape carefully after paint has dried.  Some paints require that the tape edge be scored with a knife before removal.
• Doing any touch-up with an dense bristle artist brush.

Brushing Tips-  Spend the money and get a good brush.  Get one designed for water based paint, and from a dependable company.  I like Purdy, Wooster. and Corona brushes.  A good brush will cost $12-20, but totally worth it.  

Tip 2-  Leaning to fan the brush is the secret to those professional edges.  A good way to practice is with a dry brush.  Press the brush until it fans out, now pull the brush in a straight line.  Now with paint on the brush, make sure that you gently work up the edge with the paint then pull the brush along the edge. 

Tip 3- Saving the brush.  Clean the brush by running water through the bristles, then folding the bristles toward you with the water running.  Do this to both sides until the water runs clear.  Now place the handle between your hand and spin the excess water out. Reform the bristles and place the brush back in the cover.  It is now ready for the next project.  

Rolling Tips-  Use a sturdy roller frame, not the cheapest you can find.  A sturdy frame allows even pressure to be used creating an even finish.  Second, use a natural lambs' wool roller cover 3/4" nap is my preference on all wall texture types.  The 3/4" allows for easy touch ups, and the natural wool holds a ton of paint.  Holding more paint means less dipping, which means less work and faster results.  The best thing of all is that the natural wool cleans out easy.  The wool cover can last a long time if taken care of.  The cost is more, but well worth it.