I think your best bet is to identify someone friendly in the group and ask him your questions. Every group is different and, even within a given group, you'll find that different people have different attitudes about etiquette. You'll also find--or at least I have--that guys are often more inclined to help a female cyclist than a fellow male cyclist. Chauvenism or chivarly? When I need some help on a windy day, I really don't care! I'm just sure to be profusely thankful for their help.

At my training ride, there are days that they're willing to slow down for someone who's falling off the pack and other days where everybody is just out for themselves. When it's the latter, it can be frustrating, but I've learned to just roll with it. Thankfully, our training course is marked so if you fall off, you can easily find your way home. The same holds true for flats. We usually just ask if they have everything they need and then the pack moves on. If the weather was poor or light was diminishing, I would prefer that at least one person hold up. I've thankfully never flatted, but if there was any doubt in my mind that I wouldn't be able to fix it on my own, I'd ask someone to stay with me. While our ride leaders don't necessarily stay with the slowest riders, they will sweep the course after the ride if someone doesn't come in as expected.

Beyond asking someone in your group for advice, I would definitely do what you can to be and feel prepared. Study the route sheet, carry all that you need to fix a flat, etc., etc., If someone chooses to help you, then great. But if they don't, then you won't need to panic. Regardless of the group's expectations, it's also up to you decide what kind of rider you want to be. I generally like to be the person who offers to stay behind with a slower rider or help someone with a flat. It's good karma in the least.

Finally, I'd note that, at least from my experience, I have different expectations for training rides than I do for more social rides. At training rdies, I expect to be on my own if I can't keep up. At more social rides, we usually all stay together. If someone flats, we stop. If someone starts lagging behind, we slow down. As you ride more and more with these guys, I imagine you'll start to get a feel for their approach to things.

Good luck and have fun!