Choose and Buy Plot
Building costs the same on a desirable plot
Cannot upgrade a plot later
Presumably you are trying to end up with a house of the highest possible value at the end of your house building project. The value of a house is the sum of the value of the land and the value of the house, but it's a bit more subtle than that. You could build an expensive large house on a cheap plot, but that will probably mean that the house value is disproportionally low. When budgeting for building a house, it is tempting to try to save money by buying a cheaper plot, but it's not the best strategy. It costs the same to build a house on a desirable plot as it does to build on a cheap plot. If you're going to go to all the trouble of building a house that you're proud of, make sure you start with a plot you're proud of, even if you have to spend less on the actual house. You can always upgrade the house when you've saved up more money, but you cannot upgrade the plot.
Live the plot
Need be prepared to put up with some hardship
It is highly recommended that you live on the plot during both the planning phase and certainly the building phase. You will be able to plan better if you're waking up every day on the plot and really getting in tune with it. Obviously doing this is not easy to arrange. If there's an old house on the plot, and you are not building in the same location, then that might work, but often a more viable way is to get a second hand manufactured home (a "Double-Wide") and live in that while you're building. If it's a very old cheap one, you will of course need to be prepared to slum it for a while, but hopefully the excitement of building your dream house will see you through the hardship.