I started this guide as a quick go-to for not well known tips, tricks, or things just not explained well in-game, if at all. If you have any other tips, or tricks not mentioned, please let me know ^.^

- Remember nearly everything can be destroyed when your in building mode [v]. Walk around in this mode while inside your settlment. You can scrap cars, light poles, tree's, and even the collapsed buildings in sanctuary to make room for more.

- While Building if you click and hold E, you can move your mouse to fine tune the placement of an item. This way you can make things fit snuggly against a wall. - Holding E and using scroll wheel will make it move up/down.

- Think Big: It seems there is not a limit to what you can build. You could technically make the entire area of Santuary 1 massive building 10 stories high, able to hold hundreds of inhabitants, with machien gun nests, and automated missile launchers around the entire outside.. use this unlimited building to your advantage! (Edit: There is a size limit to settlements, however 2 tips below remove this building limit for unlimited potential)

- There is currently a way to bypass the item cap limit of settlements. Follow these steps:

1) Go to a settlement, go into your workshop screen and pull up the item which you wish to place. Press ESC to exit when you have it highlighted.

2) Go to your inventory, and drop a piece of junk onto the ground in your settlement. Any junk will do.

3) Go back to your workshop screen, and destroy the item you just dropped for materials. Before doing so, be sure that you have the item you wish to make highlighted (and have all the components).
You can repeat this process as needed, hope this helps! I know it helps me a ton! Was so happy to figure this little trick out. I just hope that they don't change it, I like violating the settlement item cap and putting tons of stuff in there. It is really necessary if you wish to fully furnish all your homes/areas. Hope this tip is useful.

- Another way to Bypass this limit size is this: http://www.nexusmods.com/fallout4/mods/132/?

Follow the directions to permenantly set your size limit to 0, regardless of how much you build. Unlimited building.

-If you drop junk on the ground for displaying/decorating purposes, go into workshop mode and you can select them and move them around easier than the old method of holding down the action button and moving them. This works for almost every surface, except where it is most needed, the store shelves.

-The tier 3 trader kiosks don't fit under a 1 story roof, you'll need to make a second story above them.

Settlements depending on their size seem to have a "maximum" size they can hold. (Not confirmed yet). However, Sanctuary seems to be nearly limitless (again not confirmed yet).

To help quicken settlers to Santuary, the largest area to build by far, you can set up every other Settlement to be able to safely defend, and grow to their maximum size. When they reach close to, or their max, you can tell some of the settlers to move to another settlement.

Once you own 5+ settlements, going to each of them every few days, and sending 5+ settlers to Sanctuary can quickly make Sanctuary a big metropolis.

- There is a perk for Settlements. The first level allows you to setup supply lines between them, ultimately sharing your resources between Settlements. Don't over look this!

- Settlers who are not assigned to anything, will automatically savange for extra building materials.

- Settler Cap per settlement is 10+1 point/cha...meaning the effective settlement limit is 21.

- Sending a settler to another settlement creates a "trade Route" between them, or a connection. This connection shares resources automatically between the settlements once setup. Use this with new settlements, by sending a settler from an already established one, to the new settlement for instant access to all of your stored junk.