You either:

• Just got KF2, or
  
• Started leveling the new Gunslinger class

Unfortunately,

• You die. A lot.
  
• Your team is wiped several rounds before you even get to the boss.

Ever since the new maps and Gunslinger class were added, there's been a pattern I see in nearly every server I join, regardless of the difficulty level:

• Anywhere from three people to the entire team are Gunslingers
  
• At least one Gunslinger is far too low level for the server's difficulty level (e.g., lvl 1 on Hard or higher)
  
• Basic coordination is out the window
  
• Team members are killed due to lack of basic gameplay knowledge

In the following sections, I'll show you how to avoid this "inevitable party wipe" nexus of bad choices. You'll have more fun, get more chieves, and earn respect by being a useful team member.

* Replace Gunslinger with the new class du jour.

You don't need to become some KF2 nerd who knows every little factoid, but you should know the basics. Google "kf2 strategy", and read at least one guide on whatever class you're currently leveling.

"Little Tips That Could Save Your Life" is up to date, and isn't really that long since most of it is screenshots.
https://steamproxy.net/sharedfiles/filedetails/?id=425843240

If you can't be bothered to read all that text for a game you just started, here's the most basic and distilled set of "don't get killed out of nowhere" tips that come to mind. These are things that will get you and your team killed if you don't know them, and may not be obvious:

• Scrakes will auto-rage on higher difficulty levels, once the number of total Zeds is less than 5. If you avoid Scrakes until you have nothing but Scrakes at the end of the round, you are probably going to party wipe.
  
• Scrakes and Fleshpounds will rage as soon as their HP goes under a certain percentage (this gets lower at higher difficulties, so one shot can rage either Zed). Do not attack and enrage these Zeds if you can't personally kill it / your team doesn't know you're attacking it / your team is in no position to attack it (e.g., already dealing with another FP or Scrake). I see far too many enraged SC/FPs - sometimes more than one at a time - come out of nowhere because someone tagged it without alerting the team.
  
• A wounded Husk will charge and perform an insta-kill suicide if given a chance. Take out a Husk completely if you engage it. Run back, and alert your team, if you see a charging Husk. I've seen Husks kill half the party when they rush out of nowhere after being wounded by a player who didn't alert the team.

If someone in your game doesn't know these basics, don't berate, educate!

• Try to make every shot a headshot. Don't spray and pray. Set your Commando weapons to single-fire, and go for headshots as if you were playing Sharpshooter. On higher difficulties where a headshot might not be an insta-kill, use full-auto, but tap - never hold down. You'll kill more quickly, and save ammo. This is mostly a Commando rule, but I recommend applying it to everything. Use the pistol irons, and take a fraction of a second to go for the headshot. You will find that it takes less time to just line up a headshot vs firing half a dozen bullets at center of mass. Exception: big Zeds that need to be hit with the damage hose. Exception to the exception: the Zed Collector .500 can kill SC/FP with just a few headshots, so it's worth lining up the headshots if you have enough distance.
  
• In the first couple of rounds, it's OK to run around looking for ammo. It's also OK to be stingy with your Dosh, as you don't need armor, and you may not even need better guns for the first two rounds. However, investing in your teammates is as important as investing in your own kit in later rounds. If you are on, say, round 7/10, and you have $2000 in your wallet while the Support doesn't have an AA12 yet, you need to help a brother out. If you have spare Dosh after buying guns + filling all your armor and ammo at the Trader, donate to teammates who need it. If your teammates die from no armor, or have underpowered weapons, they can't help you survive the round.
  
• In the final Trader intermission, do not be stingy. You can't take it with you, because this is the final round. Spread around any Dosh you didn't use. A broke teammate with inadequate armor/ammo/weapons can't protect you from the end boss.
  
• I shouldn't even have to say this, but don't gank weapons. Goofus picks up the dead Medic's gun and sells it to get a little Dosh; he then dies because the Medic couldn't get anything good the next round. Gallant picks up the Medic gun, says "I'll hand it to you at the trader", saves the Medic from hunting for the dropped gun, and everyone survives the next round.
  
• Don't beg for Dosh in early rounds. You don't need the Zed Collector in round 3 when you're a level 0 Gunslinger on a Suicidal server. Get gud if you really want high end guns early on, but you don't need them.
  
• Try to ask for Dosh with specific requests, like "need $300 for ammo please". You won't sound like a whiney kid begging for a candy bar in the checkout queue, and teammates will know you're spending the dosh on something that ultimately benefits them.

I understand that it can be tempting to:

• Level on a perk trainer map
  
• Join high-difficulty games as a low-level class in order to rapidly farm XP

Unfortunately, if you level on a perk trainer, you aren't going to know the maps. Shooting Zeds in a cage is nothing like kiting through Farmhouse or Black Forest. Playing on new maps on low difficulty when you are low level will give you the opportunity to explore the maps without the threat of Suicidal / HoE insta-kills. If you level on a perk trainer, it shows. A level 25 Gunslinger who constantly dies and doesn't seem to know the map is a dead giveaway. Don't be that guy. You'll effectively be a level 1 player on a Suicidal / HoE server, which is no fun for you (because you keep dying) or your team (because you cause more Zeds to spawn, but you can't balance them out).

Similarly, joining a Suicidal server when you are level 4 is... well, suicidal. You'll annoy teammates when you die with 150 Zeds still on the map. Many players will be hesitant to give Dosh to a low-level player who is likely to just die early in the round. Don't waste your time being dead for most of your playing session.

The only exception is a very good Medic. Even a low-level Medic can be welcome on a high-difficulty server when nobody else is playing Medic. However, you will need to stay on top of healing your teammates! Don't expect a free lunch.

I recommend moving up a difficulty level about every 5 perk levels:

• 0-5 = Normal
  
• 5-10 = Hard
  
• 10-20 = Suicidal
  
• 20-25 = HoE

This is just a rule of thumb, and there's some leeway if you are surprisingly good (e.g., if you are just now leveling Gunslinger, but you are maxed out in everything else + have 100+ hours in the game). You should not be playing above Hard in the single digits, though! Moving up from 0 to 5 only takes an evening of play, and 5-10 only takes a couple afternoons of KF2. You'll be at 15+ in no time, and by playing the real maps, you'll have the skills and knowledge to go with the perk level you've earned. You'll find that Hard isn't that hard, and will tend to stick with Suicidal.

I've found I'm often on a team where I'm the only person with a mic - or even the only person communicating anything at all. Without basic communication, you run the risk of, say, an enraged FP coming out of nowhere and wrecking your team.

• Get a mic. The Zalman Z1 is about $7 online; maybe $10 with shipping. It's a decent clip-on mic that attaches to your headphone cable. You don't even need to buy a basic gaming headset.
  
• Test your mic levels, and make sure everyone can hear you loud and clear before you start talking strategy. Use push-to-talk, don't have your TV blasting commercials on open mic, etc.
  
• If you can't use a mic, try to get across critical info through text. "fp" = Fleshpound. "sc" = Scrake. Just typing "2 fp" can save the whole team from a pair of inbound FPs.
  
• The built-in "REQUEST HELP" and so on are vague, but you can use them if that's all you've got time to type. Try not to spam the voice commands. If you cry wolf all the time with "REQUEST DOSH, REQUEST HELP" x 100, you are never going to get assistance when two FPs are DPing you on the other side of the map.
  
• "REQUEST HEALING" is not for when you've got 80 HP and just want to top it off. The Medic will get to you. Ask to be prioritized by the Medic only when you are under fire and about to eat it. Don't cry wolf.
  
• If you get lost, or if the team is otherwise broken up, let everyone know where you are. "I'm at the barn", "I'm at the tracks", "We're all at the Trader", etc. is sufficient.
  
• If there's a Scrake or Fleshpound, everyone needs to know (a) its status and (b) where it is. For example, "raged sc in riverbed", or "2 fp main street".