Practice and keeping your hands warm in cold conditions.
Practice is the only thing that can get you to relax when trying to spread your fingers to play the chords, hammer down and basically remember where to put your fingers and when. As for the picking and strumming hand, the same thing applies.
You cannot go from a couch potato to an Olympic athlete overnight, you need to practice, to tone the muscles, develop stamina and be able to do what you need to do almost without thinking. The same goes for playing the guitar or any other instrument.
Although playing the guitar does need you to toughen your fingertips - which on its own takes time, you also need to develop the motor skills to develop the fluidity and range of skills necessary to produce the range of notes and harmonics that only come with practice.