When I was a young mage at level 60 having pretty much quested to that level and not having grouped much I had no idea that my talent spec was rubbish and my dps was terrible as I was ok at killing non instance mobs. I got a wake up call while going for some attunement or other when I HAD to join a raid. It was a 10 man in UBRS. Within 20 minutes the damage meters came up and the raid leader asked me if I wanted to be kicked. I asked why? He said look at the damage meters......I was 8th. I was a mage and I was 8th. Terrible. BUT at the time I didn't realise that was bad, I didn't realise that as a mage I should have been #1 or #2 because no-one told me. He whispered to me "learn2play nub" As soon as I found out what was expected of me I went and read everythng I could about magedom and my DPS increased substantially, my cc was great via a macro and also discovered that I wasn't supposed to be a selfish bastard but actually offer people water/food and a portal at the end.

So I think it's about managing expectations whether they are family, friends or not. Real friends will not get offended if you make a comment ie I had a warrior at level 18 and grouped with a bunch of RL friends from work in the deadmines. The very next day the guy who introduced me to wow said that I was the single worst tank he'd ever seen and he was right, I knew he was right and didn't take offence.