How do I choose width for a set of text fields?

Question

A programmer myself, I find it hard to make certain seemingly simple design decisions.
Currently I'm sketching a signup form for a website, and I want to keep the design really simple.

There are several sections in the form, which I decided to be best separated by horizontal lines:

However I'm really not sure about:

• widths of the text fields
• widths of the separators

I think it's best to keep the width consistent for at least elements of the same type (see above).
Is this a common practice?

Should I also align separators with the fields, or maybe with the header?
Are there any commonly accepted recommendations on this?

Answer 1

Best practices in this kind of situation are:

• Labels right aligned with right edges precisely aligned vertically.

• Left edges of fields and separators precisely aligned vertically. Also applies to the left radio button.

• Fields the same width except where it makes no sense (as in your second field).

• Length of the rules (separators) isn't critical, but they will make the most sense if they're the same width as the headline.

• An imaginary box around the entire form should be offset from the left or centered to correspond with the layout of other pages on the site.