Personally, and only because I speak from experience in doing this is to spend some time in the appraisals section of the forum reading some posts, trying to figure out values of domains and reading the posts of more experienced members and see what they look for.
Some are good at technology domains, some are good at geographics, some prefer brandable domains, some prefer commenting on high value killer keywords and I prefer exact match product domains.
While you are doing that I would hang around looking through closeout domains
(DO NOT BUY ANY YET!!!!), these are those that haven't had anyone pay their registration fee so Godaddy tries to dump them to the highest bidder first; but the ones that make it to this closeout stage are first come first serve. And yes, you can get some phenomenal domains here from time to time.
I would not buy any more in the next 6 months but read all you can, go through closeouts to try to identify those that might be interesting and then read some more. What this will do is hone your eye to such an extent and train you to look deeper than what your heart rushes into and after time you will be able to pick winners with far more consistency; or at least pick those that might have someone pay what you bought it for so you do not lose money lol
If you absolutely must buy domains in the early months then restrict it to ONE per week, see if you can find the best you can in closeouts and ignore all others.
The best will not necessarily be a .com, or even a .net. It may not be a single keyword or in a high competition field...when you see it you will know
(To shamelessly toot my own horn again, the domain in my signature was a reg fee domain that dropped through Godaddy with no one seeing it, I picked it up for $2 and there should be no problem with making $1000 on it for the one who can find the right end buyer; it fits the extension perfectly in a high competition field with great CPC revenue and could go to pretty much any lawyer in the world. I didn't even think twice about it)
Oh yeah, whatever you do keep well away from buying anything that looks like a TM name:
If you see something like faccebook.com it is a no go.
If you see G0ogol.com it is a no go.
If you see Mocrosift.com it is a no go.
You get the picture, they will cause you nothing but grief
I know you are likely chomping at the bit to get going and buy everything under the sun that you think is likely to make you a fortune but that is the quickest way to lose money; you have to remember one rule, what you buy this year you have to pay for next year to renew...if you buy 100 domains this week can you guarantee having $1000 to renew them this week next year?

Slow down, take your time...there are millions of domains out there for everyone, it is not the jackrabbit that wins the race but the tortoise that is building a tripwire device.