First an important reminder. You must use a solar filter to photograph the sun at all times and during all stages of the solar eclipse with the exception of the 2 minutes of totality.
(Ignoring the eclipse for a moment, if you are an experienced landscape photographer you know it is possible to photograph the sun safely at sunrise and sunset on those days when most of the sunlight has been scattered by atmospheric dust and moisture.)
It also makes a difference if you are using a white light solar filter or a high densioty solar filter. More about that later
Practicing for the Stages of the Eclipse Before and After Totality
Except for the two plus minutes of totality, photographing the stages of the eclipse is the same as photographing the sun now. The brightness of the surface of the sun during the stages of the eclipse is the same as the brightness of the sun now. The moon will gradually hide the surface of the sun, but the remaining visible portion will still be the same brightness and need the same exposure. This makes it easy to practice for everything but totality.
You want to work on getting the sun relatively close to the center of the frame, getting the focus right, and getting the exposure right. You also want to minimize vibrations using Live View Mode and a 2 or 10 second self timer or your images will all be blurred. The more you practice those skills now the better your results will be on eclipse day when you will be all amped-up and nervous with excitement.
There is a sunspot crossing the surface of the sun right now so that is a good test of your skills, especially your focusing skills. The sunspot should look something like the one in this cropped image. Due to the slow rotation of the sun, the sunspot will move to the right every day and eventually rotate out of sight. So work on this now before it is gone.
Practicing for Totality
Centering the sun in the frame and getting a proper focus is the same for totality as photographing the sun now. It is the exposure that changes dramatically during totality. That is the one aspect of totality that you can’t practice for ahead of time. It will help if you read this excellent and essential article by Dennis Mammana at Adorama.
Step-by-Step Articles to Guide Your Practice
If you are using a white light solar filter from Thousand Oaks Optical, read How to Photograph the Sun (and an Eclipse) with a “White Light” Solar Filter.
If you are using a high density solar filter made by anyone else, read How To Photograph the Sun (and an Eclipse) with Lee and Other High Density Solar Filters.
It is important that you know the difference between white light and high density solar filters, which is explained in the two articles. You can go blind looking at the sun through a high density solar filter, and you should never look through the eyepiece of your camera if you are using a high density solar filter. More in this article: Do NOT Look at the Eclipse Through a High Density Solar Eclipse Filter! You Could Go Blind!
Still Need A Solar Filter?
If you don’t have a solar filter and want to get one, your options are now limited. Order today while you can still get a solar filter (or solar filter material to make your own). Read this article: Back in Stock Before the Eclipse! Solar Filter Sheets Made by Thousand Oaks Optical! and this article: You Can Still Find Eclipse Binoculars, Glasses, and Photography Filters If you Act Now
So get out there, practice, and have fun! And be careful out there.
The Great American Eclipse Series
How to Photograph the Total Solar Eclipse – by Dennis Mammana at Adorama
How to Tell If Your Eclipse Glasses or Handheld Solar Viewers Are Safe – the American Astronomical Society
Reputable Vendors of Solar Filters – the American Astronomical Society