In no particular order of importance because they are all important: Proper size battery cables - absolute minimum size 1 gauge, 0 or 00 would be better; clean battery cable contacts, both ends, both cables; good high amp battery, a 400 amp tractor battery is marginal at best (I use Optima 800 amp); sound starter with a clean ground to the block. All that is if "hard to start" means is cranks slow. If it cranks OK but fails to fire that's a different issue.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.