1. Rules: I would recommend on really focusing on the points of emphasis(located in the front of rulebook), also focus on the state adoptions(located in the back of the rulebook) that your state high school association adopted for the upcoming season.
2. Equipment: I would recommend logging on onto
http://www.honigs.com and taking a look at their selection of baseball equipment, clothing, bags, shoes, and all of the neccessary items needed for the first year umpire. They have a lot of different packages to offer and you can adjustment to the packages as you see fit for your needs.
3. Strike zone: Yes, it is recommended to study the rulebook involving the strike zone, but I think really the only way that umpire develops a strike zone is by getting work time after time behind the plate, so you can use to seeing pitch after pitch coming in.
4. Mechanics: Working on your mechanics in front of a mirror at your home. Lock yourself in the bathroom, your bedroom, or in your basement, and just practice every mechanic that is used in baseball, so you can see what you like, and you can adjust it to make the best presentation possible for the coaches.
5. My final recommendation is continue to do what you doing now. Ask a lot of questions to veteran umpires in your area about any aspects of the game you do not understand. No matter if it is rules, mechanics, attitudes, game situations, or what ever it may be, continue to observe veteran umpires in action, and ask a lot of questions in the process.
My partner and I are trainers for our local association and we average two - three new umpires at each of our games all through the season wanting to watch, ask questions, seek information, and just learn all that they can about umpiring to take with them to their game.
BEST OF LUCK OF TO YOU!!