I am in no way a HDR expert, not even a photography expert. But I have had some very useful discoveries and lessons help me create some great photos and I thought I would share some:)
1, Multiple exposures.
This one sounds very obvious of course. But you can create a HDR photo from 2 exposures up to an almost unlimited amount of exposures. In my experience I get much smoother and less noisy pictures when I use a wider range of exposures.
2. Fake HDR
Sometimes it's very hard to shoot a wide range of exposures and create a good looking hdr photo, for example when you have objects or people moving. "Fake" HDR images can look almost as good as real HDR photography to the naked eye. It can never create information in the photo that isn't there originally though and there will be a loss of detail and a gain of noise. This works best for photos you won't need to print too large. If you use photomatix you won't even need to create "fake" exposures and can make your photo into a 24 bit tiff file and it's ready to go. For any other HDR software you can create as many exposures as you like by using curves or levels in photoshop.
3. Noise reduction.
There's no denying that HDR photography comes at a price. At high resolutions the noise can be way too overbearing and you will most likely make it much more attractive looking by running it through a noise program/plugin. Photoshop has this built in but it's not even close to being the best noise reduction treatment available. If you are shooting/creating a lot of HDR photography you should invest in a high quality plugin just for noise reduction. I use Noise Ninja but I have also had very good experience with Noiseware, it's all a matter of taste.
4. Smudge rough areas.
Now this is something that takes a little practice and has to be done in a very very subtle way. By using the smudge tools on areas with too much noise or destroyed pixels you can get a very smooth surface. With a little training you can get a very natural result. I always double my layer and lower the opacity on both the layer and the soft brush I will be using. By doing this you're saving some pixels/surface layer that will be unmovable and therefor also undestroyable.
5. Add contrast
HDR photos straight out from the HDR software often look a little flat and gray. They lack contrast and many times appear too light and artificial. Use levels for complete control of your shadows, midtones and highlights. I often leave the midtones alone and simply add change to the shadows and highlights. I use this is a subtle way but sometimes I go a bit further for a more grungy and moody look.
6. Add back parts of your original picture.
Put your HDR photo on top of your original photograph (the one that reflects the actual scene is the most realistic way) and then lower your opacity. Just adding back a little of the original picture can make a huge difference. If you add back a lot you will get very natural looking HDR photography and this can be all that's needed sometimes. It will open up your shadows and even out your lights and create harmony.
7. Save your color treatment and sharpening for later
Don't mess with the saturation slider when creating your HDR, just focus on the picture in itself. Don't work on your color and sharpness until you have treated your photo with both the HDR software and the levels. And just like always, sharpening is the very last step.
8. Experiment with blend modes
I often end up trying out different blend modes to add back some spice and pop to the picture. This can sometimes even replace your level treatment and add the contrast necessary. "Overlay" and "soft light" are my favorites and sometimes I even use them with a very slight blur if the picture is too sharp looking.
9. High pass sharpening
I end with using a low high pass sharpening on a duplicate layer put on "hard light". I only use it enough to bring out some details but not enough to bring back the noise we carefully removed before. I want the picture looking smooth but not blurry.
10. Inspect your photograph
This is very important, especially if you're going to print it later on. Make a close inspection of all areas, both in 100 percent size and smaller. If you find areas too rough they might need some more treatment such as noise reduction/smudge/blur.
When it comes to picking the right HDR software for you, it all comes down to taste. Photomatix is by far the most popular choice, but many people don't like how surreal and unreal the pictures can come out. This can of course be prevented by using the settings in a way that suit you and to bring back some of your original picture. Many people tend to take it too far and create science fiction looking pictures with sharp halos and over saturned colors.
There's a new HDR software out there called Ariea HDR MAX that in my opinion create more natural looking photos than photomatix do. I prefer photomatix choices and sliders though, and HDR MAX is still new enough to come with a few unwelcome bugs.
A completely free but very powerful program is "qtpfsgui". It might have an impossible name but it makes it very easy and possible to create stunning HDR photos for no cost at all! It comes with a lot of choices, and you won't lose anything by trying it out and see if it's for you!
I'm going to finish by advising you to put some time into experimenting with your settings. Find a treatment that work for your photography, mix and match photos and opacities and blend modes, and maybe even try applying different strengths in two layers and then combine them in a way that suits your taste.
Just remember that there's such a thing as taking it too far. When you process your images keep an eye on the light and shadows balance, don't make the shadows too light or the lights too gray.
I think the key to beautiful HDR photography is to not overdo it and simply use it to enhance good photography. Some pictures look good with a powerful treatment but most gain a lot by using a little.
I hope you have got some useful tips to try out!:)