I have a 590 as well.
My go to is the 3M SS pads, you can find in any grocery store. My grates still look brand new with a scrub every once in awhile. This is good for the insides and outsides.
In reality, for a pellet smoker, these are the necessities I do each cook:
1. Regularly cleaned burn pot.
2. Regularly cleaned thermostat probe
3. Regularly changed out foil or scrubbing of drip pan
4. Regularly cleaned grates
For the "looking for something to do" Saturdays, all of the above plus:
5. SS scrub of the areas surrounding the lid
6. Vacuum out the ash around the burn pot (this is where I put it when I clean out the pot)
7. Good degreasing of drip tray and catch and tube
8. finally a good soapy water in a spray bottle with a towel cleanup.
If you've had some high heat with some burning fats/oils and a good creosote buildup, I'd take the SS scrub brush to the entire inside too. If not, I'd leave it be.
BarKeepers friend is excellent and really cleans it up, but I hate the mess it makes. They have a new squeeze bottle with liquid that's better, but still too much hassle.