Darkness is a criminal's cover. It provides a burglar with time to break into your home even if you have other security measures. To deny an intruder the cover of darkness, you can ensure the lighting outside of your home is sufficient to light up doors, windows, and any other places of entry.
Floodlights provide the most security. The lighting should be intense enough that your neighbors can see an intruder or suspicious person within 100 feet of the dwelling, but not so bright that it disturbs their peace and privacy. Sometimes floodlights on opposite corners of a house can sufficiently illuminate all openings, but it is wise to have some degree of lighting on all four sides of the house for adequate light deterrent. Of course, different homes will require different lighting. This is a conservative and very safe approach, you will have to determine the exterior lighting needs of your location.
Leaving these floodlights on all the time would prevent a burglar from having the cover of darkness, but it would also be more expensive and could become annoying for people inside trying to sleep, etc. Motion activated lights are a better alternative so the lights only come on when activated by movement. Be sure that nothing obstructs the sensors, and be ready for your lights to come on with animals triggering them. (Where you live will determine this. We have dogs, cats, squirrels, and deer that come into our yard regularly.)
Hopefully you have a well-lit street in front of your home. If you don't, it is more important to ensure your entranceway (Drive way, sidewalk, etc.) is well lit so you won't encounter any unpleasant surprises when you arrive home after dark. (Leave these on if you know you are coming home after dark, or use a timer.) The better lit the front part of your property is, the more safe it will be. Encourage neighbors to do the same, and report any burned-out street lights.
It is a good idea to always have your front door adequately lit. However, leaving your porch light on all the time isn't always the best option. Besides the expense for those on a budget, it also looks better for alternate light sources to be on at different times. A criminal that is scouting the neighborhood won't know if you are coming or going, or just when you'll be home or not this way. The goal is to confuse the would-be intruder. Sometimes lights are on, sometimes off, and at other times they come on with motion sensors. This could be enough for a criminal to pass on by and look for an easier target.