I understand that the people you play against will change, but your list will change too (at least mine will). So, the advice given for this list is for people who you will be playing against at that time if you know who
. Having an all comers list is nice, but if the person knows that they won't be seeing any 2+ armor saves or 14 armor, then you can implement this in the list.
After thinking about this some more I can come to realize there are three different types of the people that come on and post a list, they most likely
: A) new to the game, B) played a while but want to try something new (tactics or army) or C) are entering a tournament.
For people in the A section, they will most likely know who they are playing since some person, or people, got them into the game. The advice in what to put in the list will also hint at tactics that would be best against their favored enemy
. If they haven't played before they may not be able to supply some of the other answers and this one point would be helpful.
People in the B section may be trying new things or a new army. If they are trying new tactics then the validity of this new idea can be tested if the most likely opponents are known. If they are trying a new army, then specific units may be more helpful than others. Being a CSM player, a good example would be to advise not bring Thousand Sons if you know that they will most likely be playing Nids, Dark Eldar or Guard. Although this one is pretty obvious to somebody familiar with the codex, but somebody new wouldn't neccessarily see it.
Lastly, the people in the C section. Sure the other questions are kind of answered if the person is entering a tournament, but again, every piece of info about what the list is for, goals, things they will not really listen to or whatever. Those are pretty much the four most important things to think about when posting a list.
I'm sure I could probably expand these ideas further to make an FAQ. Right now, there are no stickied pages on any List Forum. Oftentimes people will do things like list specific upgrade costs or other bad techniques. If there was an FAQ or something to help first time posters make a helpful list thread. I'm not saying I should
be the one to do it, but having one would be good.