Two word Keyword Domains could be studied first, along with one word generics. This will give you an understanding of the subtle or blatant valuation differences each character makes in a name. As mentioned by
@GreatBrand.in avoid spending money to start with.
Consider the purchase of a domain as one side of a trade. You would need a clear exit plan (who to sell to, why and where) BEFORE entering into any other kind of trading. With domains it's even more important because the liquidity is so low. i.e on an average of 2% sell through rate per year, you would need 50 good domains (to make one sale). The chance of you picking up 50 out of 50 good domains at the start of your venture is very low, this is why everyone on here says to study first.
One last thought. I am a trader in other areas as well. I've learned to trade by taking the excitement out of it. In this way, each situation can be looked at without emotional attachment.
Good luck!