posting pictures

Posting pictures has gotten easier on the forum but I still have trouble getting them to come out correctly. Some have taken my feeble offerings and corrected them and I appreciate it. The only thing the site says when posting them is that they must be less than 256. The last one I posted was only about 200 but it came out way too big for the screen. Can we get some guidelines for success? I would like to feel confident about posting them in the future.
Thanks in advance.
F

[Pa]

I will look into the instruction photo posting issue. Pa

Thanks Pa