Board Gameplay:

Since the areas along the side of the board are the cheapest, these tend to be the most contested. A four player game can quickly get out of hand due to the limited space there, and looking to the center of the board can be a good thing, even though these areas are more expensive. Other players are less likely to interfere with your building plans, as they in most cases the only benefit for them is that they will stop you, not gain more control themselves.

Corners are where most clashes happen, and if you choose to start on one, make sure you build plenty of houses there, to avoid losing control over it.

If you want to build larger houses for more income, corner areas are not the most suitable areas to do this. Instead, consider doing it in areas where others are less likely to interfere with your building plans. This is usually areas that don't cross another player's path, or expensive ones.

Demonstrators have two major roles: The most obvious one is to stop a player from winning, by blocking a crucial area, or stop them from taking over one of your areas in their path. There is, however another use for them early on in the game, and that is to direct the path other players take. If you are in an early position, you can for example, force them into the more expensive areas by blocking a corner area, or stop them from going into your path by placing a demonstrator in their way. Once they have taken chosen another path, they are less likely to come your way.

The thief is usually an expensive and random way of getting extra rooms, but it has the added benefit of removing rooms from your opponents, as well as maybe saving you from taking another turn in the factory (or force you opponent to do so), which can be crucial in the end game.

The Bulldozer's role is to give you enough space to take over an area. Due to the randomness of it, you can't be sure of its effect, but naturally; the more crowded the area is, the more effective it is. You can also use the bulldozer to deny opponents income from money generating areas, or try to force them to go on the defensive and rebuild areas that become weak from bulldozing.

Room Building:

While you should try to finish as many rooms as possible in the factory, you should consider the layout of the rooms. Having too many doors on rooms can be a big hurdle when trying to build houses with them. It's generally a good tactic to limited multiple doors to one type of room, and then only have one, or two doors on the rest of them.

Having a good mix of rooms can also be a saver once you get to the house building stage. Having too many of one type may flood the slots with that type, making you lose valuable time before they are replaced, or forcing you to ditch some of the rooms.
Placing doors on the short ends of rooms make them more likely to fit with any other room, this tactic, generally gives houses a larger 'footprint', however, which might not be a problem early on, when rooms are quite small.
Doors on inner corners of bent rooms generally makes the room harder to match with other rooms.

House Building:

Usually you can start with any type of room with out much problem, but if you get to choose, pick a room with several doors. This increases your options when placing the coming rooms.

Whether to finish one house before starting on the next is a matter of how confident you are. Building two or more houses at once of course gives you more options when placing rooms, just keep track of how many rooms you have so you don't end up with 3 almost ready houses and no bedrooms left!

Where you place houses is also a consideration. Remember that the Bulldozer will pick a row, or a column of plots to wreak havoc in. So if you place all your houses on a single row or column, you are less likely to get hit by it, but when you do get hit, the damage is much greater! On the contrary, if you spread your houses across the area, you are more likely to get damaged, but the impact will be less.

Should you spread the house over several plots to reduce further options when building? It might be good to 'lock down' an area when there are few plots left on it, but early on it's a pure gamble. You don't know if you're the one needing that final house to gain control of the area. You're also more likely to get hit by the Bulldozer.

Large or small houses? Large houses generate more income, but they still only count as one house, so it might be worth to consider where you decide to build larger houses. In a contested area, you could easily lose a lot of income due to someone building several small houses, so build them in 'safe' areas.