• If you're sharp (too high) lower the note by turning the tuning peg to loosen it, making it lower, until you get it to the proper pitch.
• If you're flat (too low) then you need to raise the note by turning it smoothly up, creating tension on the string and making the note higher. Keep turning it until you reach the proper pitch.
• You can also match the guitar to itself, to a piano, or any other instrument to match the pitch. If you're playing with a trumpet player, ask for an E and play until you've matched the pitch.
  

NOTE:-

Identify the correct tuning pegs. Follow each string up to the corresponding tuning peg to make sure you know which peg to turn to tune each string, and which direction. Before you consult a tuner, pluck the string a few times and turn the peg to make it go up (clockwise) and make it go down (counterclockwise).

Invest in a good quality chromatic guitar tuner. The easiest and most accurate way to tune your guitar properly is to use an electronic guitar tuner that reads your tone, usually provides a visual gauge of how on or off of pitch you are, and tells you which direction you need to tune. It does everything but turn the pegs for you. Here is an example of how to tune guitar using tuner, electrical tuner.

Using Your Android or iOS
There are many apps available in google play or iStore you can use to tune your guitar and with a good accuracy.

Pitchlab tuner

https://play.google.com/store/apps/details?id=com.symbolic.pitchlab&hl=en

Hands-free tuning for guitar and other acoustic instruments. esigned for novices and pros, fully featured, 100% free.

Unique features help you work out the chords to new tunes, visualize the pitch and consistency of the human voice, violin or other instrument, or answer the questions "what notes am I humming", "what are those chords", "am I hitting all the notes in tune", "is my vibrato consistent" etc. Select from a list of common instrument tunings or quickly create and manage your own using the built-in tuning editor.