Do not attempt any of the below should you be weak of heart, small of courage or not as unkillable as William Wallace. To Illustrate: Wallace "Kills men by the hundreds. And if HE were here, he'd consume the English with fireballs from his eyes, and bolts of lightning from his arse." This is a film quote. However, Wallace did kill and then skin Hugh de Cressingham in order to make a new scabbard for his sword.
Step One: Find yourself a cause
In Wallace's case, raping and killing your woman is, quite rightly enough to send him over the edge. What the English don't realize is quite who they're fucking with here. It's the equivalent of someone inadvertently punching Mr. T when he was a child.
Step Two: Raise an army
Not quite satisfied with slaughtering enough Englishmen to sate any average Scot, Wallace then went on to raise an enormous army of kilt-wearing, haggis-munching, caber-tossing Scots to go and kerb stomp Edward the first into yesteryear. As with most armies, he had to start small, picking off the occasional Englishmen here and there until finally clashing at the massive battle of Stirling Bridge in 1297.
Step Three: Shout Something People Will Remember
Many people that have led armies have contributed to this sort of thing. However, what sticks with most people from this film is the cry "they may take our lives, but they'll never take... OUR FREEDOM!' And as battle cries go that's one of the best there is.
Step Four: Die A Martyr to Your Cause
Wallace was eventually caught, probably while sleeping and under the influence of enough whisky to drown an elephant. Taken to the Tower of London, he was tried for treason, though he defended himself by stating that he had never sworn any oath to the King (true). Edward couldn't have one-man armies not loyal to him just sitting around so he elected to have Wallace killed in case he came after him again. Wallace was then hung until he was half dead, drawn (intestines pulled out) and cut into small pieces. Presumably the English thought he was a vampire and this was the only way of getting rid of him.
No, they don't fling porridge (that's Grits to anyone from the USA). Nor do they run around naked. However, it is a (possibly unfortunate) fact that the Scots were well known for lifting their kilts to stun their enemies. The mild-mannered, tea-drinking English would take offense at this, and while averting their delicate eyes, receive a claymore to the face.
The Scots also traditionally march to the strains of bagpipes. The idea of sonic warfare is supposed to be a recent one but anyone who's heard one of these will agree that they should be banned under the Geneva Convention.
Of course, there wouldn't be much point writing this without mentioning claymores. A claymore is a large sword with a v-shaped cross guard. Anyone familiar with deadliest warrior will know how awesome it is and why you should run like hell from a man with one. Another example of a famous madman with one can be found here.