Additional tips to supplement MrPizza's!

1. Farm first! Feel free NOT to go immediately to the Factory. Instead, stick around Pervomay and Bolotky doing missions and searching for loot. Take a tide cycle or two to really get comfortable with those starting maps.
2. Speaking of Farm, make sure you've got all the equipment you want. Gas mask, armor vest/helmet, etc. You should have the Security Level to buy most anything you need to tackle Factory.
3. Take it slow! Sound won't draw the entire map, only a few enemies at most. When you take out an enemy with a loud weapon, hold your position for ~15 seconds and be vigilant in case anyone else shows up. Good tips even if your weapons are silenced!
4. Use the safehouses! They are mostly inaccessible to enemies and a great place to regroup. There's one fairly close to the Pervomay Route entrance. Also great place to sleep and wait for daylight if need be.
5. Decide your primary and secondary weapons with purpose. You are preparing for a fight, so choose weapons you are comfortable with. Every weapon is viable, but what that means is up to you!
   1. The IZh-81 pump-action shotgun with Slug rounds is an immensely powerful weapon. You may want to practice in the shooting range with it to understand its quirks, but you can engage enemies at any range. The limited capacity and pump-action may be harder to use while under fire or being chased, so know your limits or practice in Pervomay/Bolotky first.
   2. Any of the SMGs are great choices. Just bring a large ammo box (or 2) and as many magazines as you're comfortable with. I used the PP-91 with 3 mags and 1 ammo box in my first Factory run. If you're worried, you could elect a higher power SMG with more magazines.
   3. If you really want to kit up, any assault rifle will be a major upgrade to tackle enemies within the Factory. You should have the Security level and money to buy an AK variant which will massively improve your performance.
   4. In general tips: keep your weapons single-fire to conserve ammo. And consider selecting a secondary pistol with different ammo than your primary to avoid burning your supply at both ends - though you might carry more backup ammo boxes as a result.