Take a little bit off at a time, you can tell when you have reached the quick because the inside of the nail will look white with a black "gummy" looking circle.
Ditto everyone saying 1x/wk. Yep I too gauge by the white center inside a black nail. When I see a white circle or triangle, I stop. If it is just a white pinhead, I proceed sliver by sliver.
I clip a triangle, sorta. I clip the side edges then the center. Do not clip up the nail in a vertical line: cut a line parallel to the end of the line. It will be slanted.
By clicking the sides, my dog can tell me if I'm too close to the quick without any harm being done. The clip itself is also quieter, smoother, and lower impact than one deep/thick cut, even though it is 3 swipes instead of 1.
The safest bet is cut just the hook end then dremel. I would rather cut too little and very frequently so my dog never has a bad experience. I got my mom's dog really good at nail clipping to the point where he would lay on his side when he saw the clippers and cheese. Too easy! Since I only visited for family events and it looked so easy, my mom and stepdad took over. Dad began fighting it. Then growling. Then snapping. Cuz they quicked him every darn time in their effort to not have to repeat the process frequently. Poor guy. They also never replaced the clippers and boy did those suckers get dull.
I got a dremel. Dogs were ok with it at first then Joey started acting up. Mostly I disliked breathing the smell and particles from the nail dust.