Use the developer console to see which block of code is not running.
Make/Change the test data in such a way that it satisfies the conditions to run that block.
If its an if-else scenario, try adding two test methods, with one satisfying the if condition and the other satisfying else condition - which result in overall code coverage.
Check this for quick hacks : https://www.apexhours.com/apex-test-class-best-practices/
I would suggest go through below link which will help.
Check this:
https://salesforce.stackexchange.com/questions/244788/how-do-i-write-an-apex-unit-test
https://salesforce.stackexchange.com/questions/244794/how-do-i-increase-my-code-coverage-or-why-cant-i-cover-these-lines
If you face any specific issue while attempting do post that here.
Thanks!
Check this for quick hacks : https://www.apexhours.com/apex-test-class-best-practices/