This CONCEPTS: post looks at the process of physically writing an army list, rather than exploring strategies on building and developing an army (covered in various other CONCEPTS: articles). I will highlight some of the advantages and dangers of the most common techniques, and I'm also going to discuss some alternatives including some unorthodox methods for different types of thinkers (visual/kinesthetic).
Why write your own when you can copy someone else's? Well, there are lots of reasons actually, and I will cover this topic in more detail in it's own CONCEPTS: thread at some point, but you could do worse than starting with a proven list to learn the ropes. The major disadvantage is the risk of not understanding how the army works, so picking up the latest 1st place GT winning list is not an 'I win' button! However, finding a list does consistently well and learning how to use it can be a great training tool, and is also unlikely to leave you with a bunch of useless models barring a bad FAQ or change in the game system (note - these are entirely possible!).
I.e. what you see if you're on the internet. Whether generated from a programme such as Army Builder, or typed out manually, this method is very common. This can be quick and efficient, and is also easy to read for your opponent or tournament organiser (TO).
Hand Written Lists
I do this a lot when developing an idea (although I will type up the list if I'm giving it to someone else). I have a sketch pad full of scribbles and ideas. I find that using different media helps access different parts of my brain when I'm designing, and list writing is no different. Forcing an idea through a pen rather than typing or copying on a computer/phone makes me look at a list in a different way, and this can trigger different ideas I may not have thought of otherwise. This leads to my secret weapon...
Short Hand vs Long Hand
As you become more familiar with your army, you will pick up the abbreviations for units. It's common to save time by writing lists in short hand, and I do this all the time too. However, one quick note is the danger of presuming that you know all the entries well enough, especially in regards to unit options and equipment. It wasn't until I looked more closely at some other people's long hand lists that I realised that I had a choice to make when swapping out weapons for a combi-weapon for my wolf guard, or that I could do this for both weapons if I wanted to. Details like this can easily be missed when writing everything in short hand.
Another warning is the pitfall of writing a list from memory and not checking afterwards. I have read horror stories of when this was done the night before a tournament, even by vetran players, then the points didn't add up and the subsequent penalty significantly affected the player's overall standing. So if you want to avoid the pain of dropping X amounts of tournament points per game or avoid the chance of playing with an under-pointed force, check and double check that list! In casual games, it also helps to have a legal list if you want to keep on good terms with your opponent, especially if you're playing a pick up game.
Sketching (with Hand Written Lists)
We play a visual strategy game, with models we spend a huge amount of time creating and painting (oh, for a world without mold lines...). The chances are that there are a good number of us that are visual thinkers (see Further Reading links if you are interested in finding out more about the different types of thinking/learning). When I started writing lists, I didn't have a feel for what any of my choices really looked like, or the consequences of their preferred deployments/roles (e.g. how much space in my deployment zone 6 or more razorbacks really took up, especially when you take into account terrain and the locations of mobile and static fire support).
So I started drawing out the units next to my hand written lists. A unit of 5 Grey Hunters and a lasplas razor would get 5 circles, i.e. 'ooooo', and a box with a turret. The attached wolf guard would be shown as a '+ o'. This was really easy to do, especially with a MEQ army. I imagine that I might have done this less frequently with an infantry horde army, but then again, this would remind me that I'd have to be moving and rolling for that many models in game and how slow that could be!
The next step was to sketch out these units in their relative preferred battlefield positions next to a list. So I would have the bottom row with backfield units, such as fire support or objective babysitters. The next row would hold the midfielders (grey hunters), the next the forward units (TWC), and finally the units that would be aiming at the enemy backfield (speeders, wolf scouts).
Developing on from this I started to add arrows to certain units, for example to flanking fire support units (rifledreads). Occasionally I would try my hand at typical deployments, drawing relatively to scale where possible.
When you don't get the chance to play a lot of games or whilst your learning the game, this sort of thing can be really helpful in visualising your army, and can quickly highlight the balance of your army across the different battlefield positions. When looking at the weight of the rows, there is a very obvious difference between a gunline army compared to a pure in your face force. This should give you the opportunity for a quick check against the strengths of your army, so a Tau army with the backfield crammed isn't to be unexpected, but alarm bells should be ringing if this happens with an assault army! Continuing with a gunline example, this technique should help flag up that you've got nothing to deny/take far objectives, or that you've vulnerable to assault and that you need some bubble wrap or tar pit units in midfield.
I could give further examples, but suffice to say that sketching out the units, typical positions and deployments should match your expectations and the abilities of your army. I found this method really useful when starting out, and although I don't do it so much now, this is because I've had more experience and familiarity with my primary force, but I would certainly do it again when getting to grips with a new force.
Models on the Table
One for people with large model collections or who find physically placing/seeing the models in front of them useful (kinesthetic thinkers). Although I haven't personally used this one as a list writing technique, I do this when I'm modelling/painting a tournament list to see how much I still have to do to complete the army (e.g. I've got all the wolves to three colours with details and highlights, but my 30+ guard infantry only have legs and torsos and I've only got X weeks to go!).
There are many ways of writing a list, and I wouldn't suggest that the techniques discussed above are exhaustive or compulsory. However, I hope this article has offered an opportunity to reflect on some of the benefits and pit-falls of the different methods, and give you the chance to consider trying something different! I'd be really interested in hearing if anyone else uses unorthodox methods, and how this has helped them improve their game.
Wikipedia definition of Neuro-lingustic Programming (NLP) - There is an extensive body of work classifying and discussing visual/audio/kinesthetic thinkers and learners. Highly recommended.