What are your favorite or most useful tack cleaning/care tips?

My best advice is good quality products, soaps, oils, renapur etc. Poor soaps are full of poor ingredients that will dry out the leather and cause more issues. 

Second, and this is more about buying, make sure you're thorough before purchasing items. I've seen more than enough tack that's cleaned to perfection but about to fall apart after one use because of old stitching. Don't sting yourself. 

1. Use. Seems obvious but the best way to soften quality tack is use it, clean it, oil it and use it again. Old tack is great as it's worn in and usually only needs conditioning. 

2. Wiping off tack after every use is the best preventative, but honestly a stiff brush or sponge is enough to remove the bad stuff. Decent saddle soap will do the job, even soaking in some soapy water if it's too bad. Just ensure it's dried thoroughly and oiled. 3. I've used a soft toothbrush to gently remove gunk and then thoroughly with a cloth/soap. There's no quick way, but more crevices means more work unfortunately. 4. I would say keeping it clean, but to be fair I rarely clean my personal tack and it still comes up nice. Do keep an eye on it, condition when necessary to prevent cracking and remove sweat immediately. 5. I've always simply used tack oil. Watch your stitching of course, but you can tell when the leather needs conditioning. Renapur is apparently a miracle product but I'm not sure of any alternatives

For my leatherwork, saddles, harnesses and bridles, if they are moldy, caked in mud or dirty beyond salvage looking, I fill my tub with bath warm water, put in ivory soap and silly place the tack in the tub to soak until the leather softens and is pliable again.

With different rags, sponges and brushes I carefully scrub the dirt off and clean the leather best as I can.  I rinse the leather once or twice them hang to dry in the tub.  After about 3 hours I use neets foot oil, mink oil or saddle soap, depending what the tack needs.   If you take overly dry leather and simply force the leather to bend, it in turn weakens by cracking and breaking because of dry rot.