How can I get better at building in Fallout 4?

Building and the settlement system is a core mechanic of Fallout 4 and learning it is beneficial in normal playthroughs and critical on survival playthroughs as it provides a safe area to store gear, restock on resources, and in Survival may be the only safe haven in dangerous areas.

The bare necessities of a settlement are beds, food, and water. Build these items wherever you deem appropriate and construct a small generator to a radio tower to encourage settler NPCs to your base.

When physically constructing these you may want to use preset buildings for these areas as they are fast and cheap to construct, and bedspace without a roof seems to give a happiness penalty in-game.

Next are defenses. You should strive to have a defense rating greater than the number of crops and units of water your settlement is outputting. Less than that number and your base will fall under attack more often. Feel free to use whatever defense system you want - under an attack you'll be the one to do most of the defense, the defense rating serves mostly as a deterrent.

Lastly, and I think this is most important, is making use of the Local Leader charisma perk. This allows you to denote settlers to create supply lines between your settlements and will allow you to use one settlement's scrap for construction while your in any connected settlement. When building this is the easiest way to get access to more scrap.

It would also be helpful to learn the formula for base attacks and the spawn point for them to stay beyond the range of an attack and know where they enter to know where to put defenses.