Proper Markup and CSS

[tharden3]

I have a few questions. I'm designing a web page to learn HTML and CSS. I wanted to know if I'm basically doing this right. I guess there isn't a right way, but maybe a better way of doing things:
- I've been using JPEG's (JPEG, JPG) and GIF (GIF) images. Both are compressed image formats, so they save load-time if I'm not mistaken. Is this good practice?
- I have used close to zero margins in my CSS. I just didn't need them. Everything looks right in every browser. Are margins neccessary?
- What other things do I have to take into account besides file compression, screen-reader accessibility, and Browser accessibility? Is there something else I should watch out for/make my website compatible with? By this I mean:
When you make a web site, it should be able to be read by a screen-reader. This is something "To watch out for when making a site". What other "Watch-out-for" things are out there that I need to keep in mind when designing?

[drhowarddrfine]

- I've been using JPEG's (JPEG, JPG) and GIF (GIF) images. Both are compressed image formats, so they save load-time if I'm not mistaken. Is this good practice?

Yes, but use PNG instead of GIF. Better file compression with improved images.

- I have used close to zero margins in my CSS. I just didn't need them. Everything looks right in every browser. Are margins neccessary?

If the defaults work for you then, no, you don't need to reset them.

[oler1s]

I’ve been using JPEG’s (JPEG, JPG) and GIF (GIF) images. Both are compressed image formats, so they save load-time if I’m not mistaken. Is this good practice?

Yes, but using non-compressed formats (i.e. BMP) isn’t an even passable option.

Are margins neccessary?

No. You are not required to have margins.

What other “Watch-out-for” things are out there that I need to keep in mind when designing?

Ultimately, the question is, is the website usable. You have to consider the possible audience (someone using a laptop, someone with visual impairment on an old crt, someone using an iphone, or someone with a text-to-speech reader, and so on. What each person wants.

I suggest you explore the topic of usability. You might have to buy some books on the subject, but if you are interested in good interface design, then it is something you should be knowledgeable about.