The radroaches in Vault 111 are easy to kill. You can save your ammo.
Idiot Savant can proc during quest completion. If you’ve got a quest that has a huge XP reward, consider save scumming. Save, turn in and wait if it procs. Reload if it doesn’t. Repeat until you get the proc.
One of the best weapons you can go for is the Overseer’s Guardian. It does double damage thanks to its two-shot property, synergizes with a Rifleman build and is easily available.
Jet is a godsend. Use it if you feel overwhelmed. Better yet, get Chem Resistant to avoid getting addicted. You can build scavenging stations in your settlements to produce fertilizer, then go to your chemistry station to create the drug.
Get a companion. They can distract and tank enemies for you. When they do, you can close in and get those headshots using V.A.T.S. or just shoot them the old-fashioned way.