As a general rule it is better to keep things simple, not just if you are a beginner. Remember the following points when you design your page:
1. Mock it up Try your design in Photoshop first (or which ever app you have) that way you can play with colours and styles without needing to refresh your journal too much.
2. Just because you can, doesn't mean that you should... try to avoid making things like the text size too small. The current journal style works well, so just start simply by changing colours.
3. Contrast is good. Making the colours of your text and links the same, or very close is bad m'kay. Make it easy for people to differentiate between things. Also, making your journal text too dark on a black background or too light on a bright background can be tiring on the eyes of the reader, resulting in them just not reading your journal!
4. Complexity-schmexity Complex backgrounds are all very well, but if they interfere with the journal text then again like point 3, you have lost your reader. Plain colours or simple gradients are fine. Remember that the text is the most important part!
5. K.I.S.S - Keep it simply sexy! You are not reinventing the wheel here, there is no point in trying to be too clever at first. The journal CSS is limited anyway so likely as not you will find you cannot do the complex overlays you are trying for.
6. It's not a competition. The initial flurry of activity over this will generate some friendly competition as people try to push boundaries. This is all well and good, but leave this to the 1337 h4x0r5 and try and do a journal which reflects your personality and style more. The journal is about you and a good journal design will help to enhance that. (unless you are me and have wierd freaky fingers and stuff and everyone thinks you are a wierdo)
For those of you who want to have a crack at it, I've collated a list of some of the more usefull articles and features floating around so you don't have to go searching.
journal stylesheet generator - by tobyf
This is the ultimate one stop shop for your journal. A great template generator for anyone that needs something simple and doesn't really want to learn the complexities of CSS.
Basic Journal Template by quinnypin
Not-So-Basic Journal Template by quinnypin
Both do what they say on the tin
dA v4 template by zacthetoad - A neat little template to make your journal look like Version 4 of dA. How very retro...
Journal Structure: a reference by thespook - A great visual reference of what the different classes represent on the page. Essential if you are new to CSS.
The BasiCSS by zikes - A good starting point for those that want simplicity.
CSS Rundown + Template by NyssaCreative - contains a tutorial to help you through the basics and on to more complex stuff.
For those that don't want to have to struggle, why not try entering the following competition:
Get Yourself a CSS Journal - Contest
being run by duhcoolies - head over to his journal to see more info.