Definitely check the sticky, as well as the gazillion other posts about this. Just offhand, if you're first starting and on a budget, I would suggest
1.Bandit signs (18x24) Handwritten(cheap)
2. Ads on Craigslist/Backpage/Kijiji, etc.(free)
3. Postcards (somewhat inexpensive)
4. A classified ad in a local paper (a little pricey)
5. Drive-by's (If you see a dumpster in front of an obvious rehab, stop inside and chat up the owner/crew)
6. Have a realtor pull comps for you for all of the cash sales in your farm area for the last 6 months. Pick a price that you feel represents investor pricing and go up to that. Then get the names of the buyers and contact them. (free, but I gave my realtor a starbucks card to thank her)
7. Call every For Rent sign that you see. These are likely landlords. If not, maybe they will be willing to sell at a discount (free and kills 2 birds with one stone)
That should get you going. Hope it helps!