For the most part being an active, helpful player is more than enough and I wouldn't worry too much - if you're already in forums, with a question like that, I'm sure you'll do just fine.
That being said here are a few nitpicky but common complaints that I've come across
The complaints I hear in game usually revolve around trade and either not helping or helping but ignoring players stated preference.
Trading- within fellowships "fair trade" is the most widely used format. Fair trade takes production costs into account so that we come out more or less even. Some goods cost more than others so a 1:1 ratio leaves one with a loss, one with a gain if not posted properly.
The rule of thumb is to post trades that show 2 stars minimum. Producing some goods from every tier of goods when possible is helpful and allows 1:1 trades. Some players try and only produce high value tier 3 goods and then expect to get "fair" trades closed when posting 100 gem for 1600marble. This does technically count as fair, posts with two stars, but is not really sustainable and does cause resentments along with imbalancing goods production in the fellowship.
Let me sum that up- 1:1=fair and good , 1:4 or 1:16= fair but not good
I tend to check the trader first thing when I log on and I close out whatever I am boosted in and producing. Then I look for what I need, then I post what I need. If you are proactive you can avoid posting mirror image trades and be helpful and keep goods moving.
When helping it is common to see the letters (C, M/H, B) in the city name. This indicates the type of help you could most use/prefer. C-culture,B-builder, M or H, main hall. With neighbors you can just hit whatever as that's gravy. With fellowship members if you want to maximize impact try to hit what they ask for and if it's culture try to determine if they just want the big items done or they hope to cut off after the bigs are polished to get something else. This process adds some time but can go a log way in building a relationship/avoiding frustration.
and nice tag btw.