There was an interesting article written by Tom Segal of the Racing Post (published in the Weekender) were he compared the difference between the form student style of selection (who he describes as the scientists), and those who use intuition (the artists). He didn’t think that either method was better than the other and how you go about selection is down to the sort of person you are.
I tend to fall between both stools. If I have enough form to go on (and for a lot of races, the amount of form available is scarce) then I will study each horse one-by-one assessing going preferences, trip, and if the horse prefers the course. Rightly or wrongly, I also use as a basis for form assessment the ratings in the RP. I consider them consistent enough to use. This is the way I study form for jumps racing and for 4yo+ handicaps on the flat. I suppose you could say this is the “scientific” method.
For the flat, I tend to follow trainer intuition. I highlight first the trainers in form for the previous 14-days. Trainers have to have had at least 2 winners from a minimum of 10 runners (unless they have a small stable). I combine that stat with having at least 40% of all runners placed (at least). So a trainer with, for example, 3 wins and 7 placed from 18 runners over the past 14-days would strike me as a trainer in form. Then I look at where his horses are running today. If he just has a solitary runner out, then that is another big plus. If that horse is sent to a track where he (or she) has a good strike-rate, and by that I mean better than 20% wins-to-runs, and the trainer must have had at least 2 winners at the track; then that is another big plus. Finally, if the trainer has travelled more than 150 miles to get to the track, then that is another tick in the box. This is my “artistic” method; it requires no form study at all.