Good fuel first and always. Clean fuel filter in the housing and a spare in the glove box just in case.
Stanadyne and John Deere cover about every base and are pretty much twin conditioners thanks to the two being in bed with each other early on in the developmental stages of fuel conditioner. The Howes is great stuff, and so is the Power Service.
What ever you get, make sure its formulated to chemicaly work in a diesel. Diesels will burn almost any type of oil, so people assume they can pour everything from transmission fluid to 2 cycle oil in their tanks for lubrication. Its not that easy.
Things to bear in mind when you hear talk of oils in fuel tanks, cloud points change with adding of oil... which is the temperature where wax chrystals form. This speeds up the clogging of fuel filters, which starves the injection pump of fuel for injection and cooling and lubrication. Injection pumps are not cheap.
The flash point is changed now because the added oil makes the fuel ignite at different times to different temps, aka ignition lag now, lower BTU as well.
Carbon residue properties of fuel is altered when oils are added. More carben in the combustion chamber is usualy the result.
Sulfer content is changed too. All oils have it. Sulfer is not a good thing contrary to belief... its the removal of sulfer that also removes a chemical bond for lubrication... the sulfer isnt the big lubricator, but does help some. It is extremely corrosive and can leave deposits on the entire injection system. Now you have water, which is a bi-product of the combustion process to begin with mixing with all that oxygen and sulfer to create... you guessed it, sulfuric acid. This is real bad news in the winter when cool temps bring rise to added moisture in the crankcase and fuel system. Worn out rings, worn out bearings etc.
The only thing you want in your fuel tank is diesel fuel, and chemicaly engineered additives specificaly formulated to mix with diesel fuel in a internal combustion ignition engine.
Another thing for cold temps and diesel fuel, keep the tank as full a possible. A tank 25% full has moisture particles forming on the walls of the other 75%. Fill up as often as you can during cold temps. Hope this helps.