I've always done by it setting a mark.
In command-mode, press m[letter]. For example, ma sets a mark at the current line using a as the mark identifier.
To get back to the mark press ' [letter]. For example, 'a takes you back to the line mark set in step 1. To get back to the column position of the row where you marked the line, use `a (back-tick [letter]).
To see all of the marks that currently set, type :marks
.
On a slightly unrelated note, I just discovered another nifty thing about marks.
Let's say you jump to mark b by doing mb. Vim automatically sets the mark ' (that's a single-quote) to be whichever line you were on before jumping to mark b.
That means you can do 'b to jump to that mark, then do '' (2 single-quotes) to jump back to wherever you were before.
I discovered this accidentally using the :marks
command, which shows a list of all marks.