As we all know, Chakra is created when two other forms of energy, known collectively as one's "stamina", are moulded together. Physical energy (身体エネルギー, shintai enerugī) is collected from each and every one of the body's cells and can be increased through training, stimulants, and exercise. Spiritual energy (精神エネルギー, seishin enerugī, English TV: Mental Energy) is derived from the mind's consciousness and can be increased through studying, meditation, and experience. These two energies becoming more powerful will in turn make the created chakra more powerful. Therefore, practising a technique repeatedly will build up experience, increasing one's spiritual energy, and thus allowing more chakra to be created.
so based on this the easiest way of developing chakra would be to do a combination of meditation and physical activity
now any normal shinobi would take years to develop ones chakra network to a specific size, eventually the shinobi will have a chakra network of a specific size
with that being said the best way would be to use Naruto's training method
SHADOW CLONES
A characteristic that is unique to the Shadow Clone Technique is that any experience the clones gain during their existence is transferred to the user once they are dispersed. This makes the technique ideal for spying, since the user can simply send a clone to spy on a target, then have the clone disperse itself without returning, to pass the information back to the user
Because of this any training done with the shadow clones will revert to the original meditation will develop spiritual energy physical training will develop physical energy in the cells and as such the chakra network will expand and new chakra will be developed
so it would be wise for someone who has large chakra reserves IE any uzumaki or senju to simply employ the use of shadow clones for meditation and physical training
the total amount of experience the user gains is multiplied by the total number of clones being used to train. For example, if a user creates one shadow clone and trains together with this clone for one hour, then dispels the clone, the user gains two hours of training in one hour so in simple terms if someone were to pop up 1000 shadow clones and train for a single hour it would be like training for 41.66666666666667 days in said hour
so if said shinobi were to train for a single hour a day using 1000 shadow clones for a single year it would be like training for 15,208.33333333333 years in that year
so you see the benefit
had naruto instead of training in simply learning new jutsu like Rasenshuriken and instead focused on magnifying his chakra network he would have developed a crap tonne of chakra
Just imagine how powerful naruto would have been if he had been using this method in the three years that him and jiraiya were gone