The best technique for brushing is to put your pup on the kitchen counter or any counter. This makes them more obedient...I guess it's the fear of heights...
Take your pointer finger and draw back the side of their mouth to expose the molars, since this is the primary location of plaque and tarter. Give them a good scrubbing. My vet said it's OK to make the gums bleed. Do all back teeth and then the fronts and canines. When you do the fronts, gently grab the beard fur and pull down the lower lip. It's all in the technique....try not to hurt the dog...they remember pain...
You will have to reload the toothbrush a few times with paste. Mine loves the chicken flavored one. If you get them used to it, they will allow you to do it without struggle. Be sure to rinse with your finger or a soft cloth. Give the pup a treat afterwards to reward the good behavior. I hope this helps.