Mantra have much importance in spirituality, religion and astrology. The power of Mantras can not be curtailed as they produce high quality vibrations that connects us with the Almighty.
Also, Mantras create vibrations that energizes a person with the powerful energy of the deity related to that specific mantra.
Mantras are scared words and Mantra chanting is very popular in hinduism .There are thousands of mantras in hindu scriptures and gives the reciter inner peace and contentment.
Mantra chanting is done for various purposes. It could be done as part of spiritual sadhana or for pleasing a deity or to get your work done like bringing prosperity, happiness, child or getting a job. Some people do it because it if they are chanted correctly, then they can bring lot of positive energy in your life.
Mantra chanting can be done at any time of day but its best to do in brahmamurtha (early morning hours) or during sandhya kaal (when sun is setting).
Many mantras are associated with the deity or God. So while chanting the mantra it helps to remember or visualize the deity. It is advisable to chant Mantras with closed eyes using a mala so that you can keep a count of chanting mantra .You should have trust and faith on mantra as well as on the deity and should do the chanting with devotion and not mechanically.
There are several hymns in Veda that tells us about different types of Mantras and their effects.
By chanting Mantras for a specific Planet, you can easily take its good effects, and eventually the malefic effects of the planet ends. Most of the popular mantras are those which are easier to chant. You should select one mantra and keep on chanting it regularly as more you chant the mantras, the more it becomes potent (sidh). Some mantras have to be chanted a particular number of times to get their desired potency (siddhi).