Before you attempt any interface edits, the following are recommended.
              [
1] Copy the default template folder (as mentioned 
here), update your 
theme settings to use the new theme, then use the default for reference.
              [
2] Backup the entire system, including database structure in case you need to start again.
              [
3] Have a good search program/utility handy. Sometimes you are looking for a specific div / class name and you can't find it. A quick search on the 'content/*theme*/' folder should find you things quicker. There are a few
              great free programs around, a few recommendations are listed below.
              [
4] Use a good quality text editor to edit files, 
DO NOT edit directly on the server. Edit and upload via FTP. Some free text editors / FTP utilities are shown below.
              [
5] Colours are the next problem. Knowing what the hex code is and where it's located in any CSS or template file. 
ColorCop enables you to pinpoint a colour area pretty quickly, just drag the eyedropper over the colour you are looking for. it's also free.
              [
6] Patience. Any developer will tell you this is paramount. If you are getting frustrated, come back to it later.
              
Note that where *theme* is used, this refers to the theme folder you are using, whether it be the default theme or your own custom theme.