Drawing people in action sequences can be tricky. When people have swords in drawings, they are usually fighting or preparing to fight. That means you need to think about all the muscles and the shape of the body in order for your drawing to look realistic. If you use a reference photo of a person holding a sword, drawing a sword fighter will be much easier.
To draw people with swords, you definitely want to start with a reference photo. This means you want to find a picture of someone sword fighting, in the pose you want. If you can't find a photo you like, then get a friend to hold a prop sword or even a yardstick, and take pictures.
The first trick is to get the body in the right stance. Ignore the clothes for a moment and concentrate on what the person's figure looks like as he's fighting. Start with the torso, then legs, head, and arms, until you get his position correct. Use a centre line down the torso to help you visualise where the person's centre line is.
Study your swordsman and think about his balance. Imagine how he's standing and think about where the weight falls. Is he balanced? Are his arms and legs equal length? Is there tension in his arms or are they limp noodles? You want your swordsman to be in the middle of fighting, which means that some of his limbs will be fully extended.
Once the body is done, now you can finally put in the clothes. They might be the same as the reference photo or different. Remember that clothes have weight and bulk; they will not be moulded to the body but will be tight in some places and loose in others. Think about how fabric stretches when it's pulled, and think about how gravity affects the drape of clothes.
There are several choices to finish your drawing. You can go over it in pen and then carefully erase your pencil. You can colour it in with coloured pencils. Or, you can keep it as a pencil sketch and continue erasing and adding in pencil lines for shade and shadow. Whichever you choose, remember to always think about the form underneath as you add the details on top.