It really depends on what you're flying and what you're facing.
This is the general idea- although keep in mind that I don't fly a race that can do it so...
The idea essentially comes down to that you have to be able to do more damage to the enemy at "close" range than he can do to you
and you have to be able to throw so much power into shields/ecm that he will likely never hack through them at longer range.
Different races are able to do it to different degress
Lyrans really can't do it- the bulk of our firepower comes from the ESG and disrupters, so if the enemy stays at rng 4 we'll usually be outdamaged
Klinks can't really do it, although some of their DB's aren't bad at it, Klink ships can usually outmaneuver anything they fight do it'd be kinda dull
Feds aren't bad at it- OL photons hurt, but they're not the best at it ( I'd usually gladly take 4 OL photons shot at me if I can guranteee a cloe range hit with 4 ESG's)
Kzin are like Feds- depending on the ship they're not bad, but not really designed for it (only ships with numerous racks should even try)
Gorn and Rom are good- generally the idea that closing is going to get you smacked with a number of plasma is a bit of a downer
Hydrans are fantastic at it, (depending on the ship) A Hydran ship generally has alot of power, an above average hull, a few fighters to laucnh when the enemy closes and those frickin Hellbores that can pound you from long range AND do even more massive damage (possibly added to that of fusion cannons) at short range.
And (as mentioned) keep in mind that it's kinda stupid to try it against anything that can outdamge you, a fed castling against Hellbores or PPD's is generally going to lose , and will likely lose against even BP plasma unless he's better at it than the plasma player is at breaking them. And ship size is (of course) important as well on one of the servers someone tried to castle some silly little Gorn boat with 2 G torps and a few phasers against my Lyran BCHP, and castling against the bigger maulers doesn't always work either.
(Except the STL.. if you ever fight a STL make sure you castle, it'll be a quick fight for you)
As for "speed is life"... yes and no. It's completely situational dependent.
I'm someone who likes to zip around tha map at spd 31, but I generally do alot better in PVP when I force myself to fly at spd 24-25.
Really both are completely dependent on what race/ship you're flying and what race/ship you're fighting.