1) Ignore sprints . If your horse misses the break, it won't have time to get back into contention. The draw can also have a significant affect.
2) Don't bet in extreme Going conditions unless you are backing a horse proven on extreme going conditions.
3) Steer clear of Handicaps . In theory, all horses are given the same winning chance, and these races can turn into a lottery (especially so as field sizes increase). Data from the database indicates that the strike rate in Non-Handicaps can be double that for Handicaps!
4) Leave the Veterans alone . In general terms, winning strike rates reduce as horses get older. Personally I won't bet on 8yo or older horses on the Flat other than in exceptional cases.
5) Back Horses in Form . As with the age of horses above, winning strike rates generally decrease as the last time out finishing position increases (i.e. horses finishing 2nd LTO have a greater next time out strike rate than horses finishing say 5th LTO).
6) Fancied Horses . The first 3 or 4 horses in the betting probably account for around 80% of winners. Only venture outside of these horses if you have strong reasons to do so.
7) Field Sizes . The bigger the field, the more chance there is that your horse won't give its true running (more chance of getting boxed in, hampered, clipping heels, etc). Paceform strike rates decrease sharply as field sizes increase.
8) Speed Ratings . If you use speed ratings, the strike rate of the top rated horses dramatically increase the more points clear it is of the second top rated horse (i.e. a horse who is 10 points clear of its nearest rival wins a greater percentage of races than a horse who is only say 3 points clear of its rival).
9) Early/Late Season. Give your bets extra consideration during the first and last 5-6 weeks of the Flat Turf season. A horse's fitness has to be taken on trust at the start of a season, and the end of season is renowned for shock results.
Following any of these hints should be enough to put the percentages more in your favour.