Step 1: Add subscription (2 min).
a) Go to your account page.
b) Choose “Games & Subscriptions”.
c) Click “+create starter account” and make a new free subscription.
Step 2: Configure WoW (6 min; need only for added subscription).
a) Make the macro for following:
/follow Main-Character-Name
b) Make the macro for assisting:
/assist Main-Character-Name
c) Enable auto-running for interaction with a target:
Go to “Settings -> Interface -> Mouse” and enable “Click-to-Move”.
d) Bind a key for that interaction:
Open “Settings -> Key Bindings -> Targeting” and add a key for “Interact With Target”.
Bind damage spells to the same keys as on the main character. Do this for mounting spells as well.
Step 3: Install multiboxing software (4 min).
There are a lot of choices but the most common variants are:
a) AutoHotKey or HotKeyNet - scripting languages. Pros: free and powerful. Cons: require at least basic programming skills.
b) IsBoxer, professional multiboxing software. Pros: tons of features and good support. Cons: paid, setup takes some time.
c) Levelbuddy, very simple keys broadcaster. Pros: no setup at all, free for newbies. Cons: only basic features, WoW and Classic only.
Step 4: Setup software (from 0 min to several hours).
It greatly depends on what you want. If you plan to close mythics or run 10 ppl dungeons, this needs a lot of setup. If you plan just leveling or farming, the macros above are enough.
Step 5: Launch 2 instances of WoW (2 min).
Run Blizzard launcher and choose proper WoW subscription before pressing “Play”.
Step 6: Enjoy your first multiboxing (all the time)!