1. Formulate what you hope to achieve, and devise a workable route to that objective.
2. Research the market if you wish to sell the work.
3. Approach the painting process in logical steps, which usually entail:
a. drawings to investigate compositional possibilities.
b. blocked-out charcoal/pencil/oil sketches to arrange tonal values.
c. oil sketches to experiment with various color schemes and harmonies.
d. preparing canvas and paint for the anticipated tasks.
e. applying paint to canvas, either incorporating the results of b and c in direct painting, or by tackling them in distinct phases.
f. varnishing, framing and hanging the work.
Yes, it does help to know what you're about. But though the objectives of painting, and even how to go about them, can all be stated in a few page:
1. Acquiring the necessary eye and manual skill takes years, and
2. Producing something significant requires individual gifts, strong personal qualities and unceasing application.
Whatever you attempt, you'll get there quicker if you appreciate the larger dimensions of oil painting techniques, and continually study the work of other practitioners, both the old and contemporary masters.
This sound advice and more along with instructional DVD's are available from http://www.oil-painting-techniques.com/ a site that is well worth a visit.