Places and times.
My main landscape goal was to capture Grand Prismatic Spring (GPS).
There are really three vantage spots I found.
The best spot by far is NOT from the parking lot of GPS.
The BEST vantage point is from the fairy falls trailhead about a mile or so south of GPS parking.
So take the trail which is on the northwest corner of the parking lot, next to handicapped parking spots.
Walk maybe a mile or less and keep an eye open for a bifurcation of the path. When it forks, take the left fork. There will be a small sign saying that the trail up is 400 yards (but seems more if you are carrying weight, and it is several thousand feet up, and I'm getting a bit old and fat too).
About midway up, there is a break in the tree line so you can get some shots (to the right/north), but that is not the prize. Go all the way up the trail, and up a few steps at the top to the observation area.
Tips:
The color of the pools depends on sky color. So if you have beautiful blue sky with clouds, that will be best.
I have read that GPS can be photographed at any time of the day, but I went around noonish, full sun, nice puffy clouds- until it started to rain!. Golden hours with blue sky will be great too.
I used my 16-35 III was perfect with a large enough field of view.
A 24-70 mm would be fine too.
Be sure that you have a polarizer filter on for best results.
If you have ND Grads, you may find this helpful.
A tripod will be very helpful. There is a handrail if you don't bring a tripod, but a tripod is a good thing.
I used a reverse ND filter with good results (3 stops).
Other notes:
Lots of bison on the trail, so watch out for them. They are ~2000 lbs and look docile and slow, but they can reach 35 miles/hr and sustain it. They have been reported to be able to jump 5' fences. Don't get close or turn your back on them. If one looks at you and bows his head down and up, even once, he is telling you that he is going to hook you and send you flying. I saw this behavior myself and the visitor was smart enough to get out of his way. The bison did not pursue him or otherwise get aggressive.
On the way up, a few hundred yards after crossing the footbridge, there is a beautiful pool on your right. If the skies are blue, the pool will be awesome. If the skies are overcast, it will be ugly. Grab a pic as can get within about 10 feet.
I found it very very helpful to use my 2X Hoodman Loup to focus in live view @ 10X since the far away structures are difficult to ensure best focus.
First pic at midway
Second pic at top
Shot with 1DXII and 24-70 2.8 II with only a polarier