Blocking an item is quite simple and can help hide slight flaws. Blocking means to steam and iron at the same time. It will flatten, help the item stay in shape, help the sides stay straight, and give your knitting a polished appearance. I crochet edging on almost everything I knit, so when I block it, the open work on the edges shows up nicely. Sometimes if the scarf is textured on the knitting part, I won't block that, but I will block the outer edges. Caution: Some yarns (& fabrics) may not be suitable for blocking as the high heat will melt the synthetic fibers. I take great care with ribbon, blocking very slowly as I go along. But natural fibers are excellent.
Items to block, scarves, shawls, ponchos, afghans......even wool skirts, wool coats.... with a little creativity even some hats.
Depending on the size of the item, my ironing board, or a towel spread out on a table works fine. If your working on a good table, double the towel to protect your top.
I keep a peice of muslin to use, but have been known to use a clean cotton pillow case. With my iron set on it's highest steam setting, I spread out the item, trying to get it in the correct shape and size. I thourougly wet the muslin and wring it out. Now I place the damp muslin over over the item, being sure the item is still properly placed. Next, placing the iron carefully onto the muslin, I steam the area, do not "iron" in a back and forth motion, place iron, pick up iron, move to the next area, place iron, pick up iron, and so on. Checking under the muslin on my scarf from time to time.
The muslin may dry out, throughly wet, wring out and move on. When I'm finished with blocking, I may have to re-do a section or two.
I hang my completed scarf to fully dry.