Offroad/MX chain replacement advice

Hey all, ive just got meself a new chain for my winter toy as the last was a bit naffed. Have got the sprockets on and just need to chop the chain at the right length, i would like to know the best position for the wheel on the swinger to judge how many links to hack out! Should i move the wheel 3 quarters of the way towards the front or on the middle marker? rear wheel off the floor on a stand for maximum travel, on side stand or someone sitting on it?

soz if it sounds a silly question, i could get someone to do it for me but i would rather learn as i intend to *service the bike myself

thanks in advance peeps
Amp








*it'll be a deathtrap