If you absolutely must bot on your own IP, make sure you keep at a normal play schedule. In general you really don't want to run for more than 12 hours at a time, with another 12 hours before your next session. Another obviously but often overlooked metric they can see is how many items you attempt to loot after your inventory is already full. If the system generates a "Inventory Full" message 400 times in an hour, your going to end up flagged.
Essentially the safest way to do it and make sure your main account doesn't get wrecked if your bot accounts ever go down is just make sure you use a secure VPN service and never connect out on your main account to the same IP.
Blizzard can tell if your on a proxy or a cheap vpn, and your playtime will be investigated if you send up enough flags.