I've also written an article about this topic, specifically focused on programming sessions.
It's helpful, but not necessary, to include your level in the subject, the kind of help you need, and your goals.
I'll reply letting you know whether I can likely meet your request, and often, I'll ask for more details about what you're looking for. If you're seeking a session on computer applications or programming, I may also ask technical questions so I can make sure that the tutoring I provide is correct for your situation and I have the right expertise.
For an in-person session, it's good to take a look at the route if you haven't been there before. If we're meeting in downtown Madison or a busy neighborhood and you're driving, I recommend having several parking places in mind.
If we're meeting online, make sure you have the meeting software we're using. I primarily use Skype, Google Hangouts, and Microsoft Teams, although I'm open to using others.
Of course, be sure to have any homework, textbooks, or assignments you want to work on.
When we both are there—whether virtually or in-person—I usually like to recap my understanding of what you wanted help with. This gives you a chance to correct me or fill in more details.
Exactly what we do depends on the kind of help you need, but usually I try to give you as many opportunities as possible to practice what we're going over and to ask questions.
I usually wrap up by asking one more time if you have any questions, outlining your next steps, and if you asked me to do something after, restating that.
I'm available for quick questions over email or, if we connected using a tutoring service, their messaging function. For longer questions or issues, you can of course schedule another session.
I'll send you a bill for the actual time taken (more information on how I bill) along with some notes on what we covered and talked about.