The big mistake made with masking tape is to simply think that putting it everywhere will stop paint going in areas where you do not want it. Unless the masking tape is placed carefully and the edges pressed down thoroughly, paint will seep under the edges leaving the rough, unsightly edge the masking tape was used to avoid.
A low adhesive tape is best and it is surprising how masking tape differs in quality. The quality is of course reflected in the price and if you use the type of tape which costs 30p per roll you will probably not get as good a job as if you use the top quality tape the professionals use.
The quality of tape is measured in the time it can remain on the walls, door or window frames before it becomes very difficult to peel off. This is also called the "clean peel" time where peeling does not leave the adhesive on the surface.
Masking tape comes in a number of widths to suit all jobs from 12mm beading inside glass paneled doors, to protecting 7 inch skirting from screed splashes.
Cheaper masking tapes should be removed in 3 hours whereas the more professional (usually blue) masking tapes can be left in place for up to 14 days without difficulty.
For masking large areas, the tape can be used to hold sheets of newspaper in place. For curved surfaces a more flexible tape can be used which is created especially for masking curved areas.
One thing needs to be remembered here; it is very very rare you will see a professional decorator using masking tape. The use of tape promotes less attention when painting detailed areas. With masking tape all over the place one can be tempted to just slap the paint on. This leads to a lack of general brush stroke care and while there is no paint on areas where you did not want paint, the overall finish is not as good as it could be because the paint has simply been slapped on.
Masking tape should be applied in strips no longer than 300mm. It is OK to overlap as long as the edges are firmly pushed down on the surface. In the images below you can see the tape being applied to a window pane, then cut into the corners, then the back of the blade is used to push the tape down firmly onto the surface. Further images show a carpet being masked, with the tape being pushed firmly down with the back of an ordinary knife. Finally you can see a surface mounted light switch being masked.
The process of painting around difficult areas without getting paint where it is not required, is called "cutting in" and proper cutting in is done with special brushes which, incidentally, are cheaper than the several rolls of masking tape designed to replace them!
A good quality cutting in brush can save you hours of taping up (and of course "untaping) and removes the possibility of a bad finish.
Practice is required for cutting in and as with every single job in the Building Industry, practice and good instruction are the difference between DIY and professional work. The job is exactly the same, the mental approach however is vastly different.