Ideally, you should give your boots a quick brush after each time you wear them outside.

Monthly, place the boots on newspaper or an old piece of cloth laid out flat on a table or counter. Use a horsehair brush and give the leather some light
buffing. The goal here is removing any loose dirt or salt particles which can damage the
leather over time.

Clean your boots with a soft damp cloth. Ifyour boots are particularly grimy, stained, or mud-caked, use saddle soap for a deep clean. Let the boots air dry for 10 minutes.

Polish renews the leather's color and provides even more luster and protection.

Cream Polish Application:
Check that the polish matches: Make sure the cream polish matches the leather, test on the tongue if necessary. Spread the cream onto the boot upper: Use an applicator brush to work the cream evenly over the entire boot, start off with a small amount then add more if needed. Using a clean horsehair brush, end with a quick buffing. Let the boots dry for 15 minutes.

Wax Polish Application:
Wrap a soft rag around your index and middle fingers and dip them into the wax.Using small, circular motions apply the polish to the boot, keep working until you coat the entire boot.Buff the boots, do a quick buffing using the horsehair brush, repeat to get a really nice mirror shine. Wax-based polish adds shine and protects your boots against salt or water. It also locks in the leather conditioner so you can extend the time that passes before it needs to be reapplied.

Removing the laces makes it easier to access hard-to-reach areas of the boot such as the tongue. Clean the laces

Place the boots on newspaper or an old piece of cloth laid out flat on a table or counter. Use a horsehair brush and give the leather some light buffing.  The goal here is removing any loose dirt or salt particles which can damage the leather over time.

Use an old toothbrush to help to remove dirt that is deeply entrenched in the welt.

Brush off dirt and salt. Place the boots on newspaper or an old piece of cloth that's flattened on a table or counter. Use a horsehair brush to give the leather some light buffing. The goal here is removing any loose dirt or salt
particles which can damage the leather over time. You may want to use an old toothbrush to help you to remove dirt that is deeply entrenched in the welt. 

Clean your boots with saddle soap. If your boots are particularly grimy, stained, or mud-caked, use saddle soap for a deep clean. 
With a damp rag or small brush, rub the surface of the saddle soap in a circular motion to create a light lather.

Next, rub the suds onto the outer surface of the boots, being sure not to overlook hard-to-reach areas such as the welt and tongue.
Let the boots air dry for 10 minutes.

Condition the leather
Give the boots a quick rub-down with a dry rag. This is to dislodge any remaining dirt or tiny dust particles clinging to the leather.

Apply leather conditioner / balm, with an applicator brush, apply your leather conditioner/balm to an inconspicuous location, like the tongue of the boot. Wait a few hours for it to dry.

Rub conditioner into the boot: Pour a small amount of conditioner/balm onto the second rag (rags made of chamois or terrycloth are ideal) and rub it on the leather. Use circular motions without pushing down hard – going back and forth along each boot. You want to get the product in all crevices and creases.

Use as much product as the leather needs. If your boots seem especially dried out or you haven't treated them in a while, you may need two, or even three applications for the boots to be fully reconditioned. However, boots that are regularly maintained may just need one quick application of conditioner. 
With a clean cloth, wipe off any excess product.

Let boots dry for 20 minutes. After they’ve rested for about 12 hours, once again give them a rub with a dry rag to absorb any remaining excess oils or moisture.
You should condition your boots often, as a general rule, condition them once every 3 months if you live in a temperate climate, and once a month if you wear the boots every day or live in a dry, hot climate.