I just finished running 15 PUG matches. I currently have 2 of my Centurions outfitted the way I want them, so I used them to run the missions. I enjoyed the vast majority of the groups. I was not trying to mimic a new player experience, that is why I did not use a trial mech.
Most of the groups I ran with were pretty good, except for 1 MAJOR flaw that will be addressed a little further down. The average pilot in these drops was better than I expected, especially considering the amount of trial mechs I was teamed with. I am seeing less of the "how do I set weapon groups" and "how do I jump" questions than I expected, and much more effective piloting. Their skill might not be as good as a long time CB player, but the raw talent does not seem to be lacking.
I see many people getting less than effective damage from their LRMs. Just because you have a "lock" does not mean the target should be engaged with LRMs. If the target is among the building of River City (for example) it can be very difficult for your LRMs to actually hit the mech you are shooting at. Try to make sure that your target is not surrounded by cover. Also remember that LRMs have a "hard" maximum range of 1000m. Any target more than 1000m away will not be damaged by your missles. Also consider the movement speed of your target. If the Jenner you are shooting at is 900m out and moving away from you, don't shoot the LRMs, he will almost certainly be more than 1000m away before the missles travel to him.
AC weapons are rather tricky right now, they require a decent amount of lead time and there is a firing delay between your mouse button and the shot. It takes some time to get the hang of them, but they can be highly effective once you do. Since only 1 trial mech currently uses an AC (the Dragon) I did not see many ACs being used, but the few I did see were not very accurate. It just takes practice, untill they fix some of the issues with ACs (but that is another discussion)
The *major* issue I have seen in most PUGs is the failure to defend the base. I think some of this is a lack of knowledge of base capture mechanics in MWO.
If you see the "BASE UNDER ATTACK" message you need to quickly consider returning to the base. If you are a slow mech and are on the other side of the map it may not be feasible to do so, but if you are able to start heading to the base then you might still consider heading in that direction. It is possible that the base is under attack from multiple enemies and the defense may take enough time for you to get there. And if the base is successfully defended quickly, then you have not really moved that far from where you were due to your low speed.
When returning to the base a helpful communication is "I am RTB" (Return To Base) easy to type, and it lets the team know that you are responding.
If you are in a light mech, or a fast mech, then you should seriously consider an immediate return to the base. If you choose to return, please communicate with the team as to what you find on the base. If your Jenner comes around the corner and sees 3 Assault mechs on the base then the team needs to know this, ASAP. In that situation, get yourself clear and then say something like "HELP 3 big on base". I know that sounds like a poor communication, but in the heat of battle (in a light mech) you really don't have a lot of time to type

When you are defending a base it is a good tactic to stand within the red lines. If there are enemy mechs on the base they are capturing it, but if even 1 friendly is within the lines then no capture can occur. This becomes very important when the base is almost captured. Stay in the base as long as possible while waiting for support. If you see (on your mini-map, or by pressing "B") that several friendlys are RTB but the base "health" is very low, then you should try and stay on the base untill you are destroyed. Take one for the team. If you step off of the base while 3 enemys are on it the base will be captured very quickly.
If there is no help available, or if they are simply too far away to provide support, then feel free to run and take the loss. No reason for a light to try and stall 4 assaults for an indefinate amount of time.
Communication is IMPORTANT in this game. You NEED your team to work together in order to win. And you need them to stay alive. You may be the best 1 vs 1 pilot in the universe, but if you take your gausscat (or streak cat, or jenner, or whatever) against a team of 8 that is working together then you are going to get stomped. Even at 2 vs 1 odds it is difficult (but far from impossible). Play to the strengths of your mech. Allow friendlys to support the weaknesses of your mech. Seriously consider using a 3rd party voice chat system, there are many to choose from and the game experience while in a coordinated team is vastly different from the comm-less lone wolf experience.
I hope I did not ramble too much, but I am sure I did. If you have any questions please ask. If you are looking for a team to play with, just hit the link in my signature, we are a pretty laid back group of all ages. No microphone required.