It is good if you use some existing templates in your company or search on google for "test plan" templates and use those.
Make sure what kind of test plan you are writing.
Make sure following items are covered
Suspention and Resumption Criteria
- 3rd party
- Manpower (resources)
- SQA Team
- Development Team
Software Configuration Management (or Build Release)
Test Automation (if you are using)
Test Summary Report
You might wish to use the IEEE829:1998 standard as a template for the test plan. You should consider the different chapter headings and decide if they apply to your context or not, and what level of detail is needed for each chapter.
One question you should ask yourself is : "who will read the test plan ?" and develop it according to the answer.
If the audience are testers or developers, the plan can be technical. If the audience are managers or customers, you should provide emphasis on the processes (the strategy) and how an adequate coverage will be provided, as well as what resources you will require.
It's a difficult balance to attain.