Note a couple of things about series 1, if you take a shower with it on, it will work but it will also be actively pushing the water out with the speaker (like what they do with the iPhone 7 now) it drains the battery big time, also the first time you set up the watch it goes through and indexes to save battery life in the future, this really cuts down on battery life too. Rule of thumb with any new device, don't judge the battery life off of the first day, a lot is going on that you don't see. Put it on the charger, make sure it's fully charged, go through two full days of wearing it, then start to be picky about battery life. As you use it you'll start to notice certain applications (especially 3rd party complications) will drain the watch quickly.
I suggest using Apple complications during the wear in period before you start using 3rd party complications, just to reduce battery drain. Then add them in one at a time and compare battery life as you enable them.
Choice of watch face doesn't make much of a difference, but how much time you leave it up does. I have my sounds set to low, and my screen brightness set to the lowest, it's still bright enough for me to see it in direct sunlight, and the added benefit of not requiring as much power to illuminate the screen. The taptic engine is also set to low (not off).