You'll assault all kinds of warehouses, boathouses, gatehouses, and outhouses in Mafia 3, among many other buildings and zones, but the same principles apply to each.
First- there's always another way in. Usually several, but get in the habit of looking for back doors, jumpable walls, and unguarded alleyways. If the site is on the water, a water approach is almost always to your advantage.
Second - pick off the outliers. There's always a sentry or two wandering on the outskirts, who can be stealth-killed or silent-shot without anyone being the wiser. And chances are that killing this goon leaves another vulnerable, who in turns leaves the next vulnerable, etc. Even if you plan to blast your way in to the main compound, clearing the perimeter keeps them from flanking you later.
Third - Don't get flanked. You're so much more powerful than the average goon that it's easy to get overconfident, and wade right into a fight. This can work, but if you find yourself caught in an open space between two heavy gunners, or maybe a few snipers, you might go down before you can take out all of them. So while you're easily a match for a hundred guys with some hard cover in front of you, avoid getting blindsided by a handful of idiots with tactical advantage.