The first stop for a new army is the Codex. I will usually flick quite quickly through the codex on first purchase, mainly looking at the big colour photos of the models. Once i have spent a while looking at the Codex photos, i will usually have a colour scheme or two in mind. At this point the process splits in to two parts:
- Normally i would get a couple of models from the army that i am collecting and do rough paint jobs on them. What i am trying to achieve is a good even look that can be replicated quickly, easily and neatly over many hundreds of models. Paint jobs usually consist of a base coat and then a wash, or in some cases a dip.
- At the same time, i would be looking at the codex to put together a basic army list. Normally i would start with the obligatory HQ + two Troops choices. To this i would add a couple of units that particularily stand out as being particularily interesting to paint. The army list would normally be around 1000Pts (as i find its a good number to aim for; there is enough scope there for a reasonable game).
Next step is to paint up the models. Generally they are painted in bulk, around 10 models at a time.
Once the first 1000pts is painted and i've had a game or two with them, ill know the army a lot better. At this stage i will start to add more units, either focussing on the things the army is lacking (for example Heavy Support or maybe some Fast Attack) or on units that i specifically want in the army. Although you dont necessarily get an "ultimate, kill everything it takes on" army in this way, i find that you do get a characterful army that you enjoy painting and playing with.
The original question here was "Which came first, the army or the list?". I would say in response, neither - the relationship between my army and the list is a symbiotic one. Each part plays against the other and influences the way the army and the list evolve.