I’ll often want to open a couple of files in Vim and then split the main window so I have one file on the left, and one file on the right. I’ve just learnt that you can tell Vim to open each in it’s own split, a vertical split or a horizontal split.

# Vertical split:
vim -O <file1> <file2>

# Horizontal split:
vim -o <file1> <file2>

It works with more than one file as well, so you could open three files, and have a pane for each.