To make your dog's visit to the grooming salon a pleasurable experience for all it is important to maintain your dogs general health and coat condition between regular visits.
To do this you should make sure that their eyes are clear by wiping away any sleepy dust daily, using cooled boiled sterile water and that their ears are clean by wiping out weekly or more often if needed. You can use specific ear wipes or ear cleaning solutions or powders for this.
You should bathe their paws in a small bowl of water after walking if they are very muddy, especially in the Winter, to wash off the mud otherwise it can dry to form hard cement like lumps in between pads causing pain during walking and even infections or cysts.
You should check daily, in the summer, for ticks as these can cause reactions in some dogs and are nasty things! If you find one you can best remove it using a tick twist remover tool as these twist the tick out safely and easily so as not to leave the tick jaws burrowed in your dogs skin. It is also advisable to keep up to date with regular flea, tick, worming and annual vaccination treatments from your vet.
If you have a short haired dog I recommend using a hard shedding brush over their body and down their legs using light pressure to get rid of excess dead hair. You can do this daily or weekly depending on how bad the hair shedding is.
If you have a medium to long haired dog you will need to brush daily using a slicker brush and comb. Starting at the back legs, move all over the body including the head and ears. Part the hair  as you brush so you brush through all the layers getting right down to the skin as this is where the matts start. Pay special attention to the ears, behind the ears and under the groin area, tummy and arm pits as these are difficult to reach places and where matts usually occur.
If your dog will not stand still, or is new to being groomed, then you can do it bit-by-bit giving them frequent breaks. It is advisable to use treats or try some peanut butter or cheese spread on a toy or a finger so that they are distracted by licking it off while you can get on with the brushing. Always reward your dog and be patient. If they are handled regularly they will learn it is fun and a great chance to bond, not a chore!
You can also brush your dogs teeth using a toothbrush and some doggy toothpaste. You can do this weekly or more frequently if required. Gently open their mouth and with the other hand brush their teeth gently. This will reduce plaque, bad breath and help keep those vet bills down!
If you do all the of above then you will have a very happy mutt - and groomer! Also their experience at the groomers will be enjoyable and avoid the groomer having to shave off matted fur, which I personally hate doing, but it is also uncomfortable for the dog and can be expensive for you.