Letter of recommendation
I'm really bad about remembering to write letters of recommendation, so if I've agreed to write a letter for you, feel free to bug me about it until it's done.
I categorically will not write a letter of recommendation, nor act as a reference, for a student I've had in only a single class. In many cases, it would be worse than no letter at all; your transcript shows that you got an "A" in my class, and in many cases, all I could add is "I have no memory of the student", or, worse, "The student constantly bugged me about the exams and extra credit, and showed no interest in the subject matter of the class."
If you've taken more than one class with me, ask me if I remember you before you ask for a letter, and if I don't, don't. I remember students for all kinds of reasons, but the reason that works the best for letters of recommendation is when you consistently ask questions, in or out of class, that indicate you are engaging with the subject matter.
If you are or were an undergraduate who has done research with me, see the next section on graduate students.
I will write letters of recommendation for every student I've supervised or mentored, either as thesis committee chair (major professor), thesis committee member, instructor of supervisory units, or informal mentor. I strongly recommend discussing with me your need for letters in advance; I like to think I write honest appraisals of strengths and weaknesses, and it's probably to your advantage to have some idea of what I think those are.
I find social media extremely valuable for keeping up with people I care about. Some of those people are former students.
I only link to people I've worked with outside a classroom setting. If you're an undergraduate linking to your professors, you're missing the point of LinkedIn: it's not a transcript displayed as a network. Volunteer, or take some supervisory units, and then you'll be able to make some worthwhile connections.
I only accept friend requests from friends. This includes a fair number of faculty colleagues and former graduate students, and a few current graduate or undergraduate students on whose thesis committees I've served or who worked for me when I was in I&IT. If you send a friend request and I don't respond, don't be offended.
I am not especially active on Research Gate. I only follow colleagues in my department, colleagues in other departments whom I know, and students and others with whom I've collaborated in research. You are of course free to follow me, but it's about as interesting as watching granite weather.
Although I have an account on Google+, I am not active there and I ignore all requests.