Does your high school have an ROTC program?
When I was in the CG they gave promotional preference to ROTC types,they were promoted to E-3 straight out of boot as opposed to E-2.Not sure if they still do it but its worth a look.
"Choose your rate,choose your fate"' is appropriate.
If you are mechanically inclined you should look into the MK rate,Engines,boilers,HVAC,outboards,hydraulics etc..
You will spend time"In the hole" or engine room if you do,most likely.But you will get lots of exposure to all types of machinery.
If Electronics interests you look into being an ET,with the world becoming increasingly more "wired"this is the rate that would give you a leg up in that field should you decide to go back to civilian life.
Be aware that some rates,like Gunner's mate,spend a lot of time on ships,a lot of sea time.
If you don't choose an "A"school you will go where they want you and do what they tell you,usually deck force or engineering.Both dept's will start you out cleaning and painting,deck will have you cleaning bird poop,scraping barnicles,sweeping decks and painting anything that doesn't move.Engineering will start you off scrubbing bilges and painting anything that doesn't move.
If you have an idea what you want get yourself signed up for it and take control of you future to the degree that you can,its still military and you will still be sent and assigned as needed but at least you will be doing it on terms you initiated.
Also,don't forget to take advantage of the benefits like college tuition,get all the info on the GI bill and thing the military offers.Its changed quite a bit since I was in,so I can't tell you what there is precisely,but from what I hear it has improved considerably.
My time in the Coast Guard was the best and hardest times of my life and I wish I could do it all over again.Wether you make it a career or not iyou will always remember you days in the CG.
My lab is still the best hunting partner there is.