The main thing that bothers me about blogs is poor balance. I know there is only so much customization one can do within certain blogging website… but you don't need much to make something look good!
CONSISTENCY & SIMPLICITY
You want your type to match your pictures. Lots of designers forget this. Consistent type throughout the whole document is important. Choose one or two type faces and stick with them. For example: I may use 14 pt, grey, bolded Verdana for titles and 11pt, black Garamond for the entry content.
Your entries, though they all may be on a particular theme, are going to be diverse. It's good to keep things as simple as possible. This allows the content to be the main focus. Your reader is going to be looking at the same layout over and over as they scroll/click through your content, you don't want them to be overwhelmed or distracted. Your blog should be readable.
You want your blog to be memorable, to have longevity. The best way to achieve this is simple, intelligent design. Something you've put thought into.
It's good to use a grid system. It makes everything visually appealing. I know that may seem stiff, but there is a surprising amount of ingenuity and originality that stems from grids. In actuality, I find it makes things much, much easier. No fuss!
And finally, this applies to all of design, look at the negative space around an object, the way it sets within/next to another object/type. Is it balanced? If it feels off, try moving things around until it feels comfortable. This will take a long time at first, but you're just developing your eye!
Here is a good website on grid systems: thegridsystem.org
And some inspiration: minimalsites.com
I hope that helped some new designers!