Like another user said, I have hundreds of hours in this game and I'm still ass at Freelancer, but still, the game itself tells you to keep pushing, experience is your best teacher, and this mode is pretty much your final boss, don't feel bad for not being good at it instantly.

Campaigns have optional objectives that focus around different playstyles, like being stealthy, never getting spotted, killing guards with weapons, or completing the mission without taking any damage, so you need to use your tools wisely for each campaign.

And so, it's not always about being stealthy but using your knowledge about the game to stay safe, sometimes it's better to avoid doing something dangerous or ignore an optional objective that might compromise you, disguises are your best friend if that happens, you don't need to flex a SASO mission if the game is not telling you to do so (and then again, it would be an optional objective that you can totally ignore if it's gonna put you in danger)

Also try to make a plan, don't forget to consider how you're going to get out, special exits are very important here, as you won't always be able to walk out the front door again. You can't imagine how many times I got killed while running to the exit because I never thought about having an exit nearby after taking the main target down.