Buddy is prone to gingivitis, so my vet told me I have to brush his teeth everyday to prevent recurrences, so going to the vet for cleanings is not an option. Before brushing, pet him, groom him, whatever is takes to relax him. The first couple of times will be difficult until he gets used to it. Hold his head with one hand, and let him taste the paste first, then start brushing, and as quick as possible to get it over and done with(this will get easier with practice). He will move and squirm and it can be difficult at first. If possible, have someone else hold him and also control his head, then your hands will be free to open his mouth. Just be carefull not to get your fingers in the way
After about 4 or 5 times, Buddy now only trys to get away at first and then he lets me do it. If possible have a vet demonstrate to you the first time. Just be gentle with the brush so not to hurt him.