Add some cool separators to your Dock

Run this command inside the Terminal:

defaults write com.apple.dock persistent-apps -array-add '{ "tile-type" = "spacer-tile"; }'

This will add a separator to the right of the Dock, even though you can't see it yet. Repeat to add as many separators as you need.

They will show up as soon as you relaunch the Dock, using the following command:

killall Dock

The separators won't be "visible" anyway, because they are just empty spaces, but you can still drag them around like any other icon.

(This is a very old trick, but I find that most people still don't know about it.)