Does your tractor have cylinder preheaters.
Are your air and fuel filters in good order?
How old is your battery, you may want to buy a battery maintainer and keep it hooked up to the battery during the week. The battery must be in top condition.
What weight oil do you have in the motor.
check with your dealer there may be a injector cleaner you can add to the fuel.
If you use starting fluid be sure to check with your dealer an insure you follow their procedures. As you can ruin your motor with this stuff.