Judy G. Russell, who writes the blog "The Legal Genealogist", has given a webinar That First Trip to the Courthouse which is an hour-long presentation on how to prepare for a courthouse trip, and what kinds of records that you might find there. Her webinar is available to members of the Florida State Genealogical Society, where she presented it last fall, and as part of the library of webinars available to Legacy Family Tree Webinar subscribers, where it is also available for purchase.
During the webinar, she recommended two books by author Christine Rose, Courthouse Indexes Illustrated, and Courthouse Research for Family Historians: Your Guide to Genealogical Treasures.
To her excellent recommendations, and those of the other community members here, I would add: prepare yourself for your trip by examining the kind of courthouse records you want to look at by going to FamilySearch and other sites and previewing the materials beforehand. Perhaps they don't have the land records you want to look at online for your county (which is the whole reason you want to go to the courthouse in the first place) but if you can look at land records from a nearby county from the same time period, you can familiarize yourself with the way the volumes are laid out, how the indexes work, etc.
For Texas Land records, for instance, consult:
You don't want to be figuring out how to use a Grantor/Grantee deed index for the first time when you are actually at the courthouse. Practice on online records at home, so you'll already be familiar with how the records are arranged once you get there.