I wrote a simple guide that works really well for melee classes:

Simple Focus-Based MultiBoxing Setup and Macros Guide

To clarify, the trick with melee is to run through the target mob with your main and then spin round with the mouse. This will put the mob between the main and the followers. If the mob moves or the followers are out of range just press the 'follow+assist' macro key again (you can mash it if you need to).

I know tons of people say melee multiboxing is hard but I've never had a problem using this system.