salt will raise it but then you have to worry about too much salt. Have a look at the bbc's webpage, there's a story about a teenager being told to eat more junk food to increase his salt intake because he kept fainting.
You'd think he could just add a bit to his food instead of eating garbage. But it could just be sensationalist reporting.
Apparently Germans are the only nation that consider low bp to be as much a worry as high.
Giulia