Summarize this article:

Verify that the gun is not loaded by putting the ramrod down the barrel and measuring the distance that it can reach. It must reach all the way to the location of the touch hole in the pan. Use your cleaning rod to clean the barrel of any black powder residue, dirt or dust that may have accumulated. While loading the gun, keep it aimed straight up in the air and avoid putting your face over the barrel at any time, even while you're loading it. Most muzzleloaders will come with a swab (a piece of cloth used to lubricate the rifle) fitted to the slot in the cleaning rod. Apply gun lubricant to the inside of the barrel. Do not apply too much, as it can get in the touch hole and prevent ignition. A thin layer is sufficient, no more than the amount of sunscreen you'd put on your face Pour black powder from your horn or flask into the powder measurer to the appropriate mark, then pour the powder from the measurer into the muzzle.  Tap the side of the rifle a few times with the flat of your hand to settle the powder. Using the smaller end of the bullet-starter, push the bullet into the barrel. Be gentle. When you get to the end of the starter, pull it out and use the longer end to push it farther down.  Use the ramrod to seat the bullet securely on the powder charge. Use a short but firm motions to seat it, don't jam it in a stabbing motion like you see in old Civil War movies. There's a mark on the ramrod that will let you know when the bullet has been seated. When that mark lines up with the end of the barrel, the bullet should be seated properly. It's important to make sure the bullet is seated firmly on the charge, leaving no gaps between the powder and the bullet. With the gun pointed in a safe direction, use your priming tool to seat the cap on the nipple. Make sure the safety is on, if your rifle has one, or that you're at half-cock, if you're using a side-lock rifle.

Summary:
Check the barrel. Lubricate the barrel. Measure your powder. Load your bullet. Load your percussion cap.