To prevent irreparable damage such as flaked, cracked, or excessively dry leather, it is important to condition your boots regularly. If you're in and out of water or mud often, you'll want to condition more frequently (once or twice a month). Do not let your boots sit for periods of time with mud, concrete powder, wood pulp/dust, fuel, or mechanical oils on them. These substances are notorious for their ability to dry, harden, and cause lasting damage to leather. Conditioning any boot will darken the color of the leather, so first test on a small section hidden away to ensure you're okay with the end result. You can condition nubuck, suede, and rough-out leathers, but it will discolor the boot even more than full-grain leathers. Additionally, nubuck, suede, and rough-out leathers aren't as susceptible to cracking as smooth, top-side leather is.
To apply conditioner to your boots, you’ll first want to take the laces out and make sure the boots are dry and clear of any dust, dirt, and debris. Take a clean, dry rag and work an even coat of dressing over the entire leather portion of your boot. You will only need to use a small amount. You can use a cotton swab or soft bristled toothbrush to get to the hard-to-reach spots between stitching and hardware. Once you cover the entire boot, let the boot rest overnight or until completely dry, wiping off any excess conditioner that didn't absorb.