I''d offer two different views from Rich''s.
First, let''s be clear that fuel can be contaminated by both crud in and delivered with the fuel by the vendor AND by bugs that grow in the tank. Rich''s advice about buying from a high-volume vendor is a good one, altho'' I''d suggest two add''l criteria: one with a big storage volume and one that proudly shows his hicap filters at the fueling station (or will show them to you), hopefully sporting clean bowls. This will eliminate most of the crud and your system should handle the balance.
That leaves the bugs. These grow at the interface of the water and fuel, which is why one should try to leave a tank full rather than partially full. Air holds moisture and that moisture will condense over time due to temp changes, and as the water begins to collect the bugs have a larger home in which to grow. Better to minimize this by keeping the tank topped, most especially during those more dormant periods like winter. Having a way to occasionally suction out the very bottom of the tank - to go ''fishing'' for the water collecting there - is another helpful step.
Diesel does lose some of its punch as it ages but, unlike gas, you can bolster older diesel fuel with an additive; these are available most anywhere and are inexpensive. Consider using one of them if you usage level seems to warrant it. OTOH I''ve burned fuel several times in WHOOSH that I know to be several years old (at least) with no noticeable sign of poorer performance...so how much the fuel is harmed by long term storage remains a question in my mind.