I've been trying to photograph my garden more this year too. Thanks go a camera upgrade; it has been fun. A few simple tips (then I'll leave it to the experts).
1) Take photos when your dahlias are in the shade - and they JUST got in the shade. That ensures that there is lots of light; but not direct light that washes out colors. Early morning or at dusk is a good time for me. I'll take shots with the sun at my back just when the direct rays are off the bloom.
2) Take photos on overcast days. Light clouds are a photographers dream. The light is still intense; but it is diffused enough to keep from getting that washed out look.
3) Just like when you take photos of a child - get to 'eye level' to take photos of your dahlias. Shots from above dahlias look ok; but more often, shots look better when you have your camera aiming straight at your bloom.
4) Pay attention to your 'frame.' Move all around the bloom to see what gives you the best angle; and the least distracting background. For dahlias, deep green foliage and buds look better than your driveway or powerlines.

Check out the photo below that I took tonight. Good light (evening), good angle (had to work at this one - best angle was looking through my ugly chain link fence), OK background - bummer that this nice shot has my cheap deck furniture.

Vassio Meggos - if the rest of you can teach me the 'trick' on keeping beetles off, and getting my blooms bigger - that'd be great!
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Thank you Honnat
What great tips!! I'm going to try them all. I've definitely been shooting into the blooms ...don't know why I thought they looked good that way?... hahaha! Since we havent had an overcast or cloudy day in quite a while, I'll try to take the photo early or later in the day!
Your shot is beautiful...the flower is nicely focused...and honestly I kind of like the background...after all that's where dahlias grow...in peoples yard....
I'll keep you posted.....then I'll have to figure out how to post it :)
Janice

I use the macro setting when taking photos of flowers. It's a little flower icon on my camera. I agree with the no direct sunlight suggestion. I also crop a lot. As long as the focus is clear I can later crop out what I don't want to get a nice up close shot.

PS. Honnat thanks for the great photo. It helped me ID a random tuber that I got from a friend this spring. :)