Instructions for Inserting Images into Posts and Pages can be found here: http://codex.wordpress.org/Inserting_Images_into_Posts_and_Pages
Generally, it’s good to have an established convention for photo size and placement within a post or page that remains consistent throughout your website.
Dimensions — the most important dimension when placing images is width, as it can affect other elements in your layout. Once a convention for image width is established, it’s best to be consistent throughout your site. Height can vary to some degree, but a consistent look is best and too much variation can also affect your layout.
Placement — placing images randomly on a page or in a blog post often looks busy and disorganized. Some good practices for placement:
- Float (align) Right
- Float (align) Left
- Full width of the content area
- A row of smaller images that fill the full width of the content area
My personal preference for floating an image is Float Right, because the reader’s eye can always return to the same place on the page to start the next line of text.
It’s good to avoid placing an image that has no float and doesn’t fill the width of your page. The result is extra white space beside your image that breaks up the page display.
Copyright — be sure you own the photos, or have permission to use them. It’s never a good idea to grab images from other websites.
Storage — photos should be stored on your web server with the rest of your website. It’s not a good idea to link to external photos on another server (website), because if that site is taken down or that content is removed from the external site, your image disappears.
Photo Links — unless you specifically want an image to link to something, it’s best to set Link To: None. If the default of linking the photo to its original is left in place, the user clicks on the photo and the larger image loads in the same page, taking the user away from the site content and making navigation confusing.
Borders/Captions — again, it’s best to establish a convention and stick with it. Whether you want borders on your images or no borders, generally stick with one or the other. Ideally, the same should apply to captions or, at least, to the default WordPress frame that comes with captions. If you want to use captions on some images and not others, it may be best to style the frame to match the rest of your images (or have your web developer do it).