If you're gonna start it on ether, make sure you have the glow plugs shut off, this is doable by removing the white wire from the top of the glowplugs relay behind and under your air cleaner box - without that wire the glowplugs controller cannot ground the relay's control circuit, and therefore the glowplugs will not get any power.

As for the actual jumping, whenever I was jumping my buddy's truck (old batteries, bad glow plugs, etc) I'd always use two sets of cables and connect battery to battery, then hit the high-idle so my alternator ramps up the power output to somewhat boost the batteries - worked like a charm every single time, till eventually he got big commercial batteries and new glow plugs and he no longer needs my services in that department Ideally, the safe way would be hooking the negative cables from both of my batteries to somewhere on his engine, and not his batteries, but then again every time I try that way the jumped vehicle refuses to start, so by now I just do it first and honestly expect it to not work at all - don't help most new vehicles have all their engine stuff covered in plastic, good luck finding a good engine ground on those...