If there is not much lightning around you may as well leave the shutter open for ages to record what little is there. This has the following advantages:
The strikes build up on the film and make the image look more spectacular.
In photos where non lightning sources of light are absent (i.e. scrub land etc) you will gather enough light for the landscape to become visible on the photograph.
The image below is an example this technique
Even in this photo the landscape wasn't exposed but at least the clouds (and their movement were).
The film speed you use isn't too critical. I use mostly 100 and 200 speed film and these days film quality is so good that you can enlarge them to 40cm by 70cm and they still look good. You could use all the way from 25 speed film up to 800 if you wanted to.
It goes with out saying that you should bring a torch. Besides being handy if your car breaks down in the dark of if you drop a lens cap it comes in handy photographic wise as well. If your camera is manual or doesn't have illuminated displays then you can just shine the torch on it to check it (i.e. aperture settings and the focus is on infinity).
The other really helpful thing a torch can be used for (and you need a fairly bright one for this) is to help line up the camera. When taking photographs with street lights in it you can simply use them to line your camera up how you want. But how do you get careful composition (and remember what I said about extraneous objects) when all you are looking at is darkness. Well you simply shine the torch on the ground in line with where you want one edge of the frame to be and then look through the viewfinder and pan or zoom to include the torch spot. Then you can check where the other side of the frame is by looking through the viewfinder and moving the torch beam along the ground until it starts going out of view (on the other side of the frame). You can then iterate using this process fine tune your composition (its faster to do than it is to say!).
You really do need to be able to transport yourself around, so you either need a car or motorbike. If you are young then you are going to need incredibly tolerant parents. If you have transport you can travel and set yourself up in the ideal spot to capture storms and also chase the storm to maximise photo taking opportunities.