It may sound silly but...learn how to wholesale deals.
Many wholesalers jump on the MLS and shoot investors the link...or copy and paste another wholesalers deal without the permission and add $1k-$3k on top of the purchase price.
As a investor, I have seen good wholesalers who know what they are talking about and know how to find the deal, and the process of closing with a seller... I have also seen some who think it is as easy as doing the "cutting-corners" methods as listed above.
A MENTOR is a great way to gain experience and knowledge and learn how it is done. Investing the time up front will make you extremely successful as a wholesaler. Many people just want the quick $1, but this is a long road to riches game, so take the time to learn how to play!
Everyone wants to do wholesales and/or be an agent these days but they don't wanna put in the time and effort in learning the #s. Understanding the numbers as mentioned in the other posts (ARV, Running costs/expenses etc..) is literally 50% of the battle and the difference between successful deals and just being another annoying guy spamming emails to buyers..
I would learn what the numbers look like in your respective market and get info by shadowing your local professionals like contractors and experienced agents.
This industry is about adding value, thats how you succeed. Find out what you can offer and if you can sell it good enough you'll have excellent results. The other 50% is consistency and follow ups, but thats a whole other discussion.