When it comes to mechanical mods, there are really only two ways to get "more power" to the coil, better batteries and better conductivity. A mod with silver plated contacts using high quality Sony, Panasonic, MNKE, etc batteries is all you can really do. If you are referring to wattage, when you say you want more power, you controll wattage on a mech by lowering your coil resistance;
W=V2/R
So, if you have a target wattage in mind, say 20w and you know that (under load) your mod can deliver 3.4 volts you leave the resistance a variable and use some algibra foo to solve for R:
3.4
2=11.56 thus 11.56/R=20
multiply both sides by R giving you 11.56=20R
divide both sides by 20 (11.56/20) = 0.578ohms
wrap a 6 ohm coil and on a fresh battery you should be pretty dog-gone close to 20w. Over time your battery will loose some of it's charge and thus you'll not be able to stay at 20w constantly without some form of regulation device like a kick (no kicks I know of can go that high) or a variable wattage or variable voltage device. only a few VV/VW devices can support sub-ohm coils, so you make a coil that will work on the device, say 1.5 ohm, substitute that new resistance into your algebra-foo to find the target voltage you'll need. if you use a variable wattage device, it's as easy as dialing in the wattage you want, and it will adjust the voltage based on the detected resistance.
hope this wasn't overly technical.
P.S. I find that there is a slightly larger voltage drop in telescopic mods, but this is only one man's experience. If you know that you'll always be using 18650 batteries, I recommend getting a mod that is sized only for that battery to avoid the voltage penalty created by the threading in the outer sleeve of the mod (this is the part that acts as the ground). Conductivity in your positive lead is important, but a good negative connection is as well.