These are two weird things to put together. But I think they are interlocked. The reasons we play determine what type of army list we design. It also determines what we expect from the game.
There are many reasons someone plays 40k. They like the modeling and painting aspect. Or you might be a fluff person and enjoy the story that unfolds from playing the game. Like wise it might just be a game that you enjoy play very competitively like in tournaments. Of course it could be some or all of these thing.
Knowing what your opponent expects from the game is very important. Competitive people want to play the meanest lists they can find and enjoying crushing there opponent into dust. Most love tournaments and find newer and meaner lists on the Internet. They want that competitive rush you get from overwhelming your opponent.
Fluff players want to play for the background and the story that can be made of it. The army lists that are made are in line with the background of the fluff. I have a friend that is a terrible player. He loves all the background. He names all the characters and paints everything. For him playing is the living expression of the story. That is the hobby for him. If my friend played a competitive player he would have absolutely no fun and probably think the guy is a jerk even though he probably wasn’t.
There are some people that just love the modeling and painting aspects of the hobby. Playing is a second thought as to what looks cool in their army. Putting a model together and giving it a killer display type paint job. These people don’t play often and when they do it is very casual and just a social activity.
I like 40k because of the fluff and the models. I have played since the Rogue Trader days in the beginning. Having played competitively in tournaments I know it’s not my cup of tea. When I play, all my models are painted and I love the aesthetic appeal of the battlefield. Also I love an opponent that is there just to have fun. The social aspect of seeing my friends is just as important.
When I design my army lists I generally like to make them balanced. So what is a balanced list? A balanced list in my opinion is one that has choices from every force organisional slot. (HQ, Elite, Troop, Fast, Heavy) These lists don’t have to be weak by any means. They usually can take on most armies and give a good fight.
What you put into your list is dictated by what army you play. But there are some general guidelines. First you need to determine what battlefield roles your units will play. For instance how do you take out armor, melee monsters, flyers, ECT…
The second thing is assigning units to those roles. Is your HQ unit a melee monster, big gun, or a supporting unit that gives buffs to another unit? These are things that need to be determined in the beginning.
The third thing is how many troops do I include in my army and besides claim objectives what will they do. I find that troops are usually the best buy in an army. Usually you want to put in at least one troop choice per 500 points in your army. For instance a 2000pt game should have at least 4 troop choices.
Fourth I think is determining what is my long-range support and what is my melee. You really need both. I find it good to be able to handle armor with both long range and up close. Make sure you have units to do both. I find it a good thing to have redundancy in an army. Don’t just rely on that killer shooting unit to take out tanks. Make sure that if that melee monster unit gets killed in turn 2 that you have something to stop theirs. Stuff like that.
Fifth and last is speed. You need to have a unit or two to be able to get across the board fast with either troops or other units. Having speed in your army and the ability to get to where you need to be to either capture or bring the pain to a unit is very important.
I find that usually you can find something in your army to handle most situations. Having a variety of units in your army with varying abilities can make your games much more interesting and fun. Also talking with your opponent and working out what types of games and experiences you are looking for will provide for a much richer and satisfying game experience.
Have fun and keep playing.