most important factors i have found
(not in any order after #1).

1. trainer

2. pedigree (true nicks is a great free site with outstanding info--plug in the sire and dam and get a free report)

3. market support

4. workouts (assess an independent clocker's report, but don't ever let them put you off a long price you fancy)

5. visual paddock inspection (if you're not versed in this, avoid it--NYRA has Maggie who is pretty decent though shouldn't be taken as gospel)

6. thorograph offers statistics not found anywhere else that are VERY solid; learn to use them

I've been ganbling for many decades; I find maiden races amonmg the most profitable. Don't be put off by them, esp. at Gulfstream winter meet and NYRA and So. cal all year.