I haven't done a ton of blocking, but since I can't wear wool I've done mostly acrylic when I do have something to block. It's true that you may not need to block it, but that's not a general rule for all scarves. If the corners are curling or there are slight width changes along the length, I would try to block that smooth. The pattern may also say something specific about what you should be doing to it when you block it (say, in terms of dimensions).
I don't think any blocking is truly permanent, especially with acrylic. But you can get it to look a lot nicer with water and warmth. I've done it in two ways: steam from a hovering iron, and sprayed water warmed with a hair dryer and left to air dry. Both have worked pretty well and not injured the yarn.
For both methods, start by pinning your piece to something flat. I generally use my ironing board; I think larger pieces can be done on a bed if you don't have a blocking-specific surface.
For the first method, use your iron's steam-burst button with the plate of the iron about an inch away from the piece. You can get closer, but don't touch the yarn with the iron. I use the cotton setting because that's what my iron is always set to anyway.
For the second method, spray the piece with water. You want it wet through but not soggy. Use a hairdryer to warm it all up (and slightly dry it), and then let it air dry. You could also use the hairdryer to completely dry it.
In either case, wait until the piece is both cool and dry before removing it from the board.