These are some of common 'errors' that I noticed while validating themes:

i) text visibility - unless it's on purpose (to make the operator logo 'invisble'), themers should ensure that all text are readable (ie. sharp contrast from the background) and yet suits the overall color scheme.

ii) theme or wallpaper? - when making themes, please try to make an effort to add some elements to the themes (like softkeys, statusbar, etc.) instead of merely doing a cut-out of the wallpaper. Common techniques incl. blurring or bevaling.

iii) wallpaper choice - a theme's main attraction is the wallpaper. Hence, a better wallpaper (instead of a dull/poor quality one) almost always lead to a better theme. Take more time to search for better wallpapers.

iv) size - learn how to the 'save for web' feature in photoshop. Also, learn when to use gif, and when to use jpgs to ensure best ratio of quality/size.

good points , but one thing which is personal choice, i don't really like beveled edges in the status bar, a colour gradient and other things i think are ok though

also the loading bar. alot of themer artists forget about this but it can throw the theme off balance.

another common mistake is to overdo the theme. sometimes the mistakes of the new themers is to put so many effects into a theme. the only thing about adding so many effects is it may look too busy. even if the blur filter is being used the wallpaper and added effects may cause the icons/text not legible. sometimes simple is the way to go.