Looking for opinion polls, found many threads on best places and various ways of doing them from going full Rambo to stealthily. Rambo mode i'm not up to. However, those who do it stealthily seem to be light on detail how they do it, beyond don't get spotted.
Pretty much any surface settlement mission where what you are doing would upset the locals is handled in the same fashion.
I found surface missions incredibly difficult before learning this as they seemed almost impossible (or to take WAY to long in the few cases where I succeeded.)
1) Local the 'Settlement Alarms' panel
2) Select it to disable the alarm
3) Engage in whatever you were supposed to do there
Some important points:
1) Selecting the 'Settlement Alarms' panel requires Level 2 authorization. You get that by illegally scanning it from one of the locals. Illegal scanning (i.e. hitting R while having the scanner out to put it in clone scan mode) is, well, illegal. So make sure no one is looking at you when you are doing it (i.e. be roughly behind the target with them facing away and make sure no one else nearby is looking in your direction.) You can scan through windows if the target is close enough, but be careful since NPCs typically are looking out the window and have pretty good peripheral vision (if they see you with the scanner in cloning mode, they instantly go hostile and raise the alarm.)
2) Once you have Level 2 authorization, you can use a nearby terminal to look at facility details to find (and mark on your HUD) where there alarm panel is located. This is really helpful in lower security installations since they can be in some odd places.
Once the alarm is disabled, the settlement is pretty much yours. The automated defenses will no longer activate (because the alarm isn't raised), and hostile NPCs don't 'share' data to locate you, so can basically run and hide from them and not have the whole base gunning for you. Also, some missions require that the settlement alarm not be raised. Once it's disabled, it can't be raised, so that mission objective can not be failed after that point.
There's a whole bunch of other nuanced 'stuff' that can impact how you do the mission (a few examples below), but you always want to turn the alarm off as soon as possible.
- e-breaches (what they can be used on, when its worth it)
- when to use the Maverick suit plasma cutter and charge tool (R) to pop a secured door open vs use a cloned authorization
- when to disable the authorization scanners on the doors vs. leave them turned on
- when to stealth kill with the charge tool (R)
- when you can get away with fast drawing and 'stealth' killing someone in the face with the charge tool (R)
- how to 'contain' a situation if you're spotted (i.e. an NPC goes hostile before the alarm is disabled) (hint: shoot them)
Oh, one more tip. Don't be afraid to run. To my knowledge, there isn't any ground mission you will fail by leaving. If things go sideways (and sooner or later they will), don't be a hero and try to salvage the situation. Just run back to your ship, take off and low wake away, swing back to the settlement and land again. The locals have really short memories so low waking out and coming back resets everything (note: any bounties you picked up will still be with you, so if you're wanted you'll want to give the guards a wide berth to avoid scans.)