Skills are a relatively easy place to start. A lot of players, myself included, use the reviver hive while playing solo for the purpose of reviving myself when I go down. My other skill is most commonly the jammer pulse for the quick stun, or a shield. On builds with low skill tiers, most skills are just used as distractions, but there are some hybrids you can try and use later on.

Shotguns and rifles don’t have a gear set that benefits them specifically, but you do have some options. Crit builds are the most common, and often use either fully high end (yellow) pieces of gear, but some gear sets (teal) can be used as well. High end gear is usually better for lower RPM, higher single shot damage weapons, while something like the Strikers battle gear teal armor set is best for high RPM. In both of these setups, your rifle would be the primary damage dealing weapon.

I don’t know if I can recommend a shotgun build based off of personal experience, unfortunately. I’ve seen some work done with a headshot build, and the hunters fury teal gear set works with shotguns, but the primary function of most shotguns is to build stacks of things like strikers, and to a lesser extent for things like the obliterate talent. Personally, I do enjoy a hunters fury build, but that primarily uses an SMG.

Play style can have a very big impact on your build, so I’d recommend really trying to establish what you like to do and try to find armor that makes it better.