If the rim has a "narrow" side ,usually the one facing the lug nuts,thats the side you mount the tires on first--whichever side the drop center is closest too..
Worst tires to mount IMO are small diameter ones like lawn tractors that dont always have a drop center--or its located dead center ,the smaller the rim diameter the harder a battle it is also it seems...I was afraid to tackle the 28" rim and tire on a 600 Ford tractor I had,but I was amazed how easy it was once I got the calcium unloaded ..I was almost able to mount the tire just by stepping on the bead and walking it around the rim,only had to use the spoon once or twice..