Due diligence just means planning ahead, but it can break you if you chose not to.
I made a small chart, as this process can be a bit back and fourth between some of these considerations. Take a look below...
So for the rewards themselves you are saving up to, there is a loyalty point database located over @Elletha. This consideration is part of the narrowing down to which specific corporation you want to run missions for.
How do you find agents? I reccomend in-game agent finder to locate the top tier agents you want to run for, which lists the systems available. You will always be able to find agents using this tool, but they may be greyed out (unavailable due to standings) or not exist - like L5 pirate trainers as shown below.
Once you have narrowed down the agent type using the filters, you can do a bit of intelligence gathering about the system and proceed to review the location.
Location is everything. Evemaps doesn't have a pinpoint location of all agents but will help you make the considerations required to prepare for the area you are considering. Which neighboring systems do you have - are some low-sec? Is the system a high-sec island. Are we deep in null and is there a safe route to a nearby trade hub so you can safely resupply or sell loot and salvage? This consideration should be done for the end-game agent mainly and not so much for the lower tier agents that will eventually get you there, as those will in almost all cases be fairly safe except for low/null agents which host most of your pirate agents or level 5's.
Type of agent relates to your choice of ship in that location of space. Bring appropriate equipment and by that I mean based on type of mission and type of opponents. You may have the upper hand where you are now in terms of specific resistance profile and damage profile, but move 15 systems over and the rats may be different and deal different damage, so bring appropriate gear and make the appropriate skill training adjustments. In case of distribution there are blockade runners you may need to consider - and when swapping from Amarr pirate rats to others, you may need to skill up on anti-jamming and dampening and change tactics for these encounters - using entirely different combat ships may be an appropriate consideration as well.
For extra bonus, keep in mind that the standings for the corporation you end up running missions for carry over to other stations and can affect tax rates when selling your phat lewts, even corp-wise.