STEP 1:
First of all open ACCOUNTsection of your gmail account.
STEP 2:
Now Click on SECURITYlink. Here you'll see ACCOUNT RECOVERY OPTION, just click on that.
STEP 3:
Now add your personal mobile number here, also add one email id [ I recommend you to create an extra email id and don't share this email id with your friends. So that , there should be no chance of hacking]
STEP 4:
Now after doing above step, go back to SECURITY link. Here you'll get 2-STEP VERIFICATION , just turn it on.
Now google will ask you to link your mobile number with your account. After complete verification, your number will be linked with your account. Now whenever a login attempt is made,a confirmation code will be sent to the number which is to be entered to gain access. This makes your account more secure.