Many of us ignore developing a testplan while testing, but it not advisable. A testplan helps us capture things such as:

• Dependencies on the software,
• Organize the parts which have been testing and which need testing, by which we wouldnt miss out any areas,
• Human Resource planning which is very important and assigning responsibilites helps us complete testing on schedule,
• An architectural overview of the application and testing approach,
• The risks associated with the applications and also the prerequisites for testing the applications.

Defining test requirements
When defining test requirements, the goal is to determine how each feature of the application is supposed to work and then create tests that exercise those features thoroughly.
It may not be practical to automate all your tests, so you should try to prioritize your automation strategy. you should considering automating if,
It will be repeated frequently
It is relatively easy to automate
It is difficult to reproduce manually
There is high risk associated with not performing the test before the
application is released