TOR is not just important, but mandatory when visiting the deep web. In fact, you can ONLY visit the deep web using TOR. It is very important to make sure your TOR browser is always up-to-date. Download the latest version of TOR at the Tor Project
The FBI is always attacking TOR with various clever zero-day exploits. Update your Tor browser or go to jail. Period!
TAILS is pretty cool. It torifies your entire computer. For most users, Tails is overkill, but if you are doing some seriously nefarious stuff on the deep web, you may consider using Tails. The problem I have with Tails is that you can’t run a VPN over TOR, which is in my opinion the best security setup. With Tails, you rely entirely on the security of TOR itself. Download Tails here: https://tails.boum.org/install/download