Those are giood ways to edit art, but you don't have to go to the HTML if it makes you uncomfortable (some are less comfortable than others). When you're in the edit window, just click on the art and the original dialogue box comes up, the one from when you first uploaded it, which includes the size box. Change the numbers there to anything that fits your layout.
I use 150 as a width and flush left (or flush right) when I'm saving space, but you can't see much.
I use 250 and flush left (or flush right) when I'm embedding art in a post.
I use 500 or 600 when I want the art to run the width of the copy (usually to accommodate a cutline and/or art credit), and leave the default setting that forces type to jump below it. Flush center achieves this as well, but I've never tested to see how that works on phones.