A large dog (or dogs) is certainly good. If for no other reason, they'll typically sense an intruder before you do.
Motion sensor lights are probably one of the biggest deterrents. Criminals hate to work in the light, and there may be uncertainty as to whether it was a sensor, or someone hearing them, etc. who turned on the light.
Plenty of reinforcing ideas you can do to external doors. Some of the easiest and best are also the cheapest. Using 3" screws for your hinges and latches, for example. Kickplate kits. Top and bottom locks.
Another one (previously mentioned), is to switch out your internal door locks with actual external locking doorknobs. This way, can make a bedroom kind of a safe room while you sleep. Anything that adds time, noise, and a barrier between you and an intruder is a good thing.
Windows are trickier. The film is a good idea (and fairly inexpensive). Bars are better of course, but have visual pitfalls. Best measures though, depend on the type of window. If you can use some kind of a bar to prevent them from opening, all the better. Another idea is to have spiky, thorny plants growing under each window. Makes it less appealing as an entry choice.
Fake security sign. So, you don't pay a monthly fee. A sign can fool folks into thinking you do. This alone could cause one to simply skip to the next house. Even if they think it may be fake, they'll think twice. For best effect, use an actual sign from a known company (especially if the same as a neighbor's), or at least one that looks real.