Everything in life needs planning. Days out, even trips to the supermarket. So it's only natural to asume that the most important thing that would need planning is work at your job. Let's not talk in the context of game for a minute. Lets thing about a builder who has a client that are a couple who own a piece of land that they want to build a house on. Imagine if that builder just got his diggers in and started digging foundations without thinking it through before starting any work. Having a blueprint of the house not only lets the builders know how the house will look, but also the clients, so they can decide if it's what they want.
Now let's look at the same example in the game industry. It would be the same for the lead artist to have a similar role as our couple in our last example. He would oversee the concept or environment artists to make sure the asset ( let's say it's a building that's going into a city environment) is going to fit not only in size but also in style. That the complexity of features such as windows and doors aren't to complex as this would result in the game running at low frames per second or worse it would crash all together.
So with this in mind what can I do to make the process of planning easier for me and the person reading it. In my opinion the most important aspect would be simplicity. I don't see the point of having pages and pages of text. Sometimes a quick sketch that's been annotated can be more than enough to get the point across, rather than paragraph after paragraph of text. Also understanding limitation and restrictions. Or even the role of the "asset". For example, if it was a enemy character for a first person shooter, he may not need to be rigged for talking in cut scenes unlike the main characters. This may mean that his mouth could be model without the need for it to be opened, thus saving valuable time that may have been wasted if this area was overlooked and not first discussed or not made clear during the planning stage.
An example of restriction would be that a model needs to be under a curtain amount of triangles. So planning a budget amount over the entire model would avoid having all the triangle used up on the first part they you modelled, only to realise as you got closer to the end you have to make it less detailed as you would have like, due to the fact you would run over budget. Equal distribution of details is important to balance the overall density of a model. This would very difficult if it was not considered during the planning stage.
It's important to get into the habit of thinking about the projects were set as a whole rather than just jumping into max and start modelling something why were are studying at university, as this will become second nature to us when we end up working in the industry.