Where do I start? Who do I go to?
Is your name on the county records (land deeds / minerals) - verify that first!
Get ahold of EOG or Marathon - they are actively drilling in Karnes CO.
Check with your nearby neighbors - Karnes co is HOT, so no doubt someone nearby is already leased.
Make sure you get 25% royalty - Karnes is right in middle of hot-spot, so 25% is no brainer.