A lot of times I'm in a situation similar to this:1. <Line 1>2. <Line 2>3. <Line 3>4. <Cursor is here>5. <I want to copy line 1 here>An easy solution is mm:1<CR>yy`mp - that is, make a mark at line 4, go to line 1, copy it, go back to the mark, and paste. Is there a shorter/more fluid solution to this? I do this often enough that I'm happy to make a mapping for it. 
How can I use a line number to copy a line to where my cursor is?
cursor movement
Looks like a case for ex copy (:help :co or :help :t)::1t4or, using your cursor's position::1t.This does not copy the line to the yank register, which might or might not be what you want.