Tips on visiting Brooks Falls as well as a comparison with Hallo Bay.
The first thing to say is that it is a magical experience to be able to view the bears so closely at Brooks Falls. While I was there there were between 8-14 bears at the falls. I saw all sorts of behaviour: fighting, mating and of course fishing as well as three bear cubs! It was like being in the middle of a wildlife documentary.
Now on to the practicalities of visiting. Because I didn't wish to commit to booking to stay in the lodge 18 months in advance I opted to stay in King Salmon. That worked well. It's only a 20 minute float plane ride to come in daily so you beat the other tourists coming from Anchorage, Homer or Soldotna. Also, I think the accommodation in King Salmon is slightly better, proper bathroom, no bunk beds, TV and wifi - in a word - luxury in comparison to Brooks Lodge - and cheaper I think! However I was lucky in that I didn't get delayed due to poor weather.
Next things to bear in mind to make the most of your visit if you are keen to see as much as possible:
Get over the bridge asap because that is where bear jams tend to be.
It takes about 5 minutes to get to the bridge from the lodge/lake landing area. The 1st viewing platform is just on the far side of the bridge. You then have a 7 minute walk gently uphill along a gravelled road. Eventually you get to a T junction for the path going through the woods. At the junction is the only loo (apart from the lodge). Then you have a 10 minute or so walk along a narrow path through the woods that leads to the walkway that eventually turns into the viewing platform. The walkway is long (it probably takes about 8 minutes to walk from beginning of the platform to the falls bit). As others have described, the walkway splits into two at the "tree house". One part goes to the lower viewing platform which tends to be less crowded. And the other to the main falls viewing area which you have to sign up for. When I went we were allowed in for 1 hour segments. As soon as you left you could sign up for another visit. The rangers said they were considering reducing it to half hour slots for next year to give everyone a better chance to see the bears. Whilst I can see the fairness of this I am not sure how well it would work because it takes several minutes to get there and back. And that, added to the setting up time of cameras/tripods or a gap on the balustrade might mean you don't see so much.
Other tips. Remember you're not allowed to take any food with you - not even chewing gum! But water is allowed. You need to be back on the right side of the bridge an hour before your flight leaves. That reduces the viewing time somewhat because you need to leave the falls about 1.5 hours before your flight.
Space in the floatplane is limited and so your camera bag or handbags will be taken off you (and put in the rear of the plane) although you can have a camera around your neck. I recommend that you do because there are often bears fishing on the lake you land on! Your first visit requires a 20 minute ranger session on bear behaviour etc. You are not required to attend the ranger session on subsequent visits. Be prepared for rain - you can buy strong plastic bags quite cheaply to protect your cameras. Bring mosquito repellant. I had a 300m lens and that worked well and I only struggled to get sharp images in low light of the bears on the far shore.
I decided to go for three days and I am glad that I did. I agonised over when in July to visit and opted for the middle of the month (15, 16 & 17th). I read so many confusing reports over when the peak of the salmon run might be I wasn't sure what was best. Someone told me that the fishery downstream releases fish irregularly which may account for the fact some days were better than others. The first day was very crowded on the platform so my time on it was limited. Some fish were jumping but for some reason the bears were not on the top of the fall - they were at the bottom. The 2nd day was quieter so the platform was less crowded (I think people got delayed by poor weather) but there weren't so many fish. The 3rd day was the best, the fish were jumping and I got the dream shot of the bear catching the fish in mid air at the top of the waterfall. But it was wet and so a lot of people were put off from staying out on the platform for long.
I attach a link to the video I made of my visit so you can see what to expect:
http://youtu.be/aBAnV73R3c8 . The video includes shots of Aialik Glacier and the Northwestern Glacier as well as a humpback whale.
I also went to Hallo Bay with Emerald Air who I highly recommend. If you can, I recommend doing both trips because you see different things. At Hallo Bay, it is a much quieter experience wandering around the meadows and spotting bears in the distance. The scenery is wonderful, snow capped mountains and lush bright green meadows. If you have a guide who knows the bears it is possible to get very close. I got to within 20 feet of a bear and her cub. We sat on a log and watched the cub play in the grass for half an hour.
I hope that's helpful