Let's see. First, equipment:
Are you diving with or without fins? Obviously technique will be different in either case. Longblade fins help, but I don't really think they're necessary to be able to make it 26 ft.
Are you wearing a wetsuit? Make sure you're properly weighted.
Now:
Breathe Up: In general, before making a dive, you have a breathe up period where you relax, lower your heart rate, and breathe. I'm not going to discuss hyperventilation. It's quite a controversial topic--know that it's out there and has advantages and disadvantages. However, that shouldn't really be an issue for the type of dive you need to do.
Starting the dive: I haven't been freediving enough to really recommend a method of making the actual dive from the surface underwater. In general, I'd say the important parts are that it is relaxed, drives you underwater, and doesn't create a whole lot of drag. From my experience, getting part of your body (eg. a leg) out of the water helps push you down thanks to gravity. I'm sure someone else can offer more specific advice for the dive. Try to stay vertical. As you submerge, spit out the snorkel, and bring your hand to your nose to equalize. Keep it there. Equalize on the surface and as you start the descent. Don't try to dive without clearing your ears or sinuses.
During the dive: Once your fins are under water, start kicking. How you kick will be dependent on what kind of fins you're using. Equalize pressure the whole way down. If necessary, exhale a very small amount into your mask to keep it comfortable and keep it from squeezing your face. Try to stay vertical--just like proper trim when scuba diving, it will use less energy, and you'll be going down, not out, meaning that you'll be descending faster in terms of depth even if the distance you swim is the same. On y our way down, avoid looking at the bottom. Look straight out, keep your chin tucked to your chest and look up, or somewhere in between. Once you think you are nearing the bottom, you can glance quickly and use peripheral vision to try to gauge when to stop your descent.
Turn:I don't really have any advice here.
Ascent:
Just like your descent except in the opposite direction. However, don't equalize on the way up. Keep looking straight out or down now, not towards the surface until you're near it. Kick until you reach the surface, and after you break it, breathe.
Good luck with making your dive and getting the job.