Having them spread evenly between different accounts is how. I have one of each class on each, and those two new accounts I just got are following the same pattern, which means when I've leveled them all to 100 I'll log on 5 at a time 11 times and do missions on each as well as refresh work orders. My time is limited, I'm lazy and I'm also getting pretty tired of it, so I try to cut down on unecessary stuff and do one thing at a time. Like dropping Barns for Trading Posts to cut down on some of the time spent, and not doing all daily profession cooldowns every single day except for when they need to refresh the work orders which the addon BulkOrder reminds me about. The multibox software I use can also broadcast mouse clicks so I just spam right click missions with MasterPlan and hope for the best. I'm planning on getting shipyards on those new characters... maybe, one day. Maybe when I have a few days off from work or when I'm working my night shifts.
And perhaps on a related note I have Asperger's and doing these garrison chores are part of my daily routine, so you could probably say that I'm literally a bit autistic about this.