Anthony... for nearly 40 years I have been in this trade.... Currently I am the shop foreman for a growing dealership... 7 bays at present with 7 more on the way...
Now, I do want to apologize for "going off" like that.... but, man.... I can't find words for what it makes me think and feel....
I realize that you must be young and new to this trade so allow me to offer some advice....
First and foremost.... the modern automobile is built around electronics. A tech needs a sound basic knowledge of electricity, it's principles, proper testing, selecting the proper test and deciphering test results. Get a good quality DMM and learn how to use it properly.... Three voltage drop tests are all that is required to almost isolate the concern.... know when to set the DMM aside and use an incandescent test lamp or a powered, low impedance test lamp or even a sealed beam headlight with test leads attached - each and every one of these tools has a use - depending on what we are doing will have us select the appropriate "weapon". Without a solid knowledge of electrical, a tech will be doomed to guessing, wasting time and will be denied the "cat bird seat". In Canada, we have an apprenticeship porogram that takes care of things like this... in the US, you will likely have to attend a college or trades school but this knowledge is vital if you desire to be a good tech.
Second... documentation.... Without the manuals, everything is going to be a guess.... very possibly an expensive guess.... If I feel that I am unfamiliar with an electrical circuit, I look at the wiring diagram first... Thursday, one of my junior techs came to me.... he had over two hours into an ABS light.... I had him show me where he was in the pinpoint test.... a glance at the circuit diagram and I had him look at all the connectors in that circuit with the advice of which connector I would look at first... the growing green death told the story. It was a retail job so we tried cleaning and protecting the connections rather than replacing harnesses... One happy customer. Knowing how the circuit works is a prerequisite for repairing it in a timely and efficient manner.
Sticking with 'documentation' for a bit.... todays engines and such are pretty "high strung" compared to their older brothers.... Proper assembly techniques and close attention to torquing fasteners is more important than ever... and is only going to become more important in the future. Workshop manuals will guide us through these techniques and show us when and where we will require special tools.....
And that brings us to tools.... A good DMM, specialty tools as required by our "customer base", a good and capable scan tool and the time to "play" with it in order to understand it's capabilities (as well as our own). We should regard our manuals as "tools", as well... Without them we might as well be without a hammer or a ratchet...
Fourth (tools was third, OK?)... knowledge.... we should endeavour to gain knowledge from any source we can. Aftermarket manufacturers often have FAQs on their websites... auto parts stores often have some sort of teaching aids on their websites NAPA, I am sure, is one.... KEM used to have some stuff on their weebsite... others are likely similar. SnapOn and MAC offer courses... yes, they are usually thinly disguised sales seminars - but there is knowledge to be gained... and knowledge is truly power... Knowledge.... build a simple circuit with a lamp a switch and a battery... practice with your DMM on this circuit... add a resistor to some point in the circuit to learn what happens when a wire or terminal corodes... put the swtich in the hot side to see how it works (DMM-wise) put the switch in the ground side (few automotive circuits are power side switched on late models) and see how that looks on the DMM. Good shop manuals include a subsection in each section called "Description and operation".... put down the Spiderman comic - lay Dean Koontz and Tom Clancy to the sode... read "descrition and operation" until your eyes hurt. Join i-ATN... read the forums.. check out the areas of the site that you are allowed to view... BATauto has some decent stuff. Look around... there's some good stuff - by no means is it everything you will need but it will be a decent start.
Now, this part could be "lastly" but there is a lot of things I haven't mentioned... so we'll call it "next".... your employer... and yours is one that needs a special sumthin' from the sound of it..... A good boss will desire his techs to learn and improve... he will endeavour to find the training that his techs need... he will give them the manuals they need and have specialty tools available.... If he doesn't do this, you will remain stuck in a dead end job.... you will never have the chance to be as good as you can be.... and you wont advance in your chosen field. The rewards are there to be had for a tech that is good at what he does and makes customers happy.... I have two diesel certified techs that will make an obscene amount of money this year because they are good at what they do and I am there to ensure that our customers are happy.... and not a BG flush to be had... I wont put up with that kind of crap...