Don't stick to just 1 nute company, mix it up.
Not necessarily good advice. I would say that your first time growing you should stick with one line. You're much less likely to run into deficiencies or overfeeding of specific nutrients if you're running a consistent brand (provided of course it's not a crappy brand). Once you have more experience mix-and-match can be useful but until then you're flirting with disaster.
Rule #1 Never use full dosage on the bottle.
That's good advice. Always start out really light and dial up. All the brands over estimate how much you'll want to use and you'll never see as big a problem from underfeeding as you would from overfeeding.
Oh and compare dif brands too. yes, AN has some good stuff, but other makers have the same product for less than 1/2 the price.
Compare like AN Rhino Skin to Botanicare Silica Blast. Same product for like 1/3 the price.
Comparing them on the shelves doesn't do a lot. You can't tell by looking at the labels which are the better product no matter what anyone tells you. Even the best growers in the world can't read a label and tell you how the nutrients inside compare to other products because the labeling laws are completely stupid. Half the stuff that makes a modern hydroponic formula good doesn't even show up on the label.
Yes, you may come across a product that might be 1/2 the price of another brand, so it sounds like a good deal, but when you read how much they ask you to use it could be 4x the amount you need compared to the other brand that may be a lil' more expensive.
This is an excellent point. Too many people only look at the price per liter of the bottle itself. Application rate is the key to knowing what you're spending. If I spend $500 on a liter bottle but I only add a drop of it to every reservoir that's actually a cheap product (exaggerating here, obviously).
So really pay attention to the labels.
Again, labels are good for some stuff, but you can't use them as the sole basis for comparison. Two different products could have identical numbers on the label but be entirely different on the inside because the laws governing labeling are so completely screwed up.