in a nutshell, the larger the value of the potentiometer, the brighter your tone will be. i usually install 500k pots to my humbucker-equipped guitars and 250k for my Strat/Tele. i tried using a 1 MΩ potentiometer with my EVH Wolfgang before and i enjoyed it for a while. it really gave me a bright tone that and it sort of functioned as a booster as well. i just changed my pot to 500k because i haven't been playing hard rock that much lately and i didn't need the "boosting." nowadays, i just use CTS or Callaham cryo pots.
i usually add a treble bleed capacitor/resistor combination in parallel with the left terminal (with the pot's back facing you) and the wiper of my volume pot to change how the pot responds. my favorite combination for 250k pots is a .001µF Mallory cap in parallel with a 150KΩ precision resistor. the highs are retained even if you roll off the volume pot and the taper response is more linear. connecting the resistor in series just lessens the current flow through the potentiometer, considerably varying the tonality while maintaining its logarithmic taper. for 500KΩ pots, i use a .002µF Mallory cap with no resistor in parallel.
the potentiometer's three lugs or legs are it's terminals. the left leg (with the knob facing you) is terminal A, the middle leg is the wiper terminal and the right leg is terminal B. the reason why the wires going to the output jack of the guitar are connected to the wiper and terminal B is because we'd want the potentiometer to have near-zero resistance (absolute zero resistance is ideal but very hard to achieve) when the pot's knob is turned fully clockwise and to have full resistance (e.g. 250KΩ, 500KΩ, etc.) when the knob is turned all the way to the left. the standard guitar pot (rotational type) has a movement angle of 270° from end to end. connecting the output wire to terminal A and the wiper will just reverse the orientation (full resistance at fully clockwise position, near-zero resistance at fully counterclockwise position).