Just read lots of news/opinions from well spoken/written sources and steel their ideas/language.
Probably a good start.
When I feel comfortable with the topic, I can start applying my own touch.
Another thing: Public speaking is more about body language than about speach content. Your feet are cement, but your arms may make motions. Appearing confident is much easier that way.
With the earlier mentioned pills, this works out quite well.
So probably no need to worry about it.
Lastly, practise practise practise. My dad routinely has to give presentations in English, despite being mediocre in it, but practise helps him out a lot. It gives confidence and will in turn make you a better speaker. Don't do it alone either, get friends and relatives to listen in and provide feedback.
I wish my parents would understand a word of english :/
Friends are probably also no option, since most of them live far away from me.
I guess I have to abuse the good ol' mirror for that...
I hear tongue twisters can help get rid of accents, you could try that.
Well I think accent isn't that much of a problem, as the English language comes to me quite naturally.
Only issue is that my vacabulary surpasses my speaking skills, which results in me choosing more difficult words, which may result in a interruption of my otherwise fluent speech.
But I think some speaking practice and a more careful selection of words might fix this.
Here are some examples of great similes based on wordplay and such.
http://www.evilpasta.com/14dx.shtml
Interesting read.
Lets see if I can use some of those for myself

(but probably not for the compoetition though)
Thank you all for your advice so far.
I start reading up on these topics tomorrow.
Still have more than a month to prepare myself for it.