Advice Bulletin No. 1 – Inserting Pictures In A Pos
First, check the file size of your picture. Uploaded images should be sized so that they do not unnecessarily consume our limited photo storage space, so that we are forced to delete pictures in older posts. High resolution pictures from your digital camera may also cause the main page to load more slowly and should be reduced to a smaller file size. Your file size should be under 100kb. Most photo management software applications (e.g., Microsoft Picture Manager that comes with Microsoft Office Suite) have a tool that makes resizing pics for web pages very easy. A WordPress FAQ on this topic is available here. The FAQ gives you links to free software you can download to resize pictures if you do not already have something.
Advice Bulletin No. 2 – Using HTML Codes to Create Special Characters
A complete list of HTML codes that create ASCII special characters is available here. If you print out this chart and keep it handy, you too can be a dork one of the cool kids by putting German words with an umlaut into your posts.
For example, to make the footnote superscript, just type ampersand-sup1-semicolon (using the symbols, and without the dashes) and you will get ¹. (Obviously, you can use whatever number you want.)
It works fine in the comments, but not necessarily in the window you usually use for main page posts. In the Write window, the code for the footnote superscript will look like it is going to work when you click Save, but when you publish your post the HTML code shows up instead of the superscript. You can Save and look at the Preview below the Write window to see if this is going to happen.
If you encounter this problem, hit the “Code” tab that is just to the right of the “Visual” tab at the top of the window. This takes you out of the Rich Text Editor so that you are just looking at HTML. You can then insert the superscript code there and the RTE won’t screw it up when you publish.
In general, if you are having trouble using an HTML code when you post, the problem may be that the Rich Text Editor does not recognize it, and you can use the “Code” tab to avoid the problem. If this doesn’t work, then WordPress does not support the code (e.g., attempting to change fonts) and you are out of luck.
Advice Bulletin No. 3 — Embedding Videos
It’s easy, as explained by WordPress FAQs on the subject:
Ignore the embed code that is used for other hosting services like Blogspot. Just use the basic URL for the video to embed it in WordPress, typing like this: (youtube=Put The URL Here) — except you use brackets  instead of parentheses ().
If you want to get fancy about embedding videos, e.g., skip some opening material and start at a particular point in the video, here are Ten YouTube URL Tricks You Should Know.