Actually you are asking two questions and they are both very important ones at that. However, you would be surprised to find out that you/or your company already have the answers to parts of both your questions. Actually the 5 questions listed below should have been answered as your business was being contemplated. 

1)  Are you clear why people should do business with you rather than your competition?

2) Who is the target market for your products?

3) What could go wrong and how would you solve it?

4) Are there additional products or services that could tie into your main offerings?

5) What are the main things you want your customers to know about you? 

Now we go to the business plan.

According to the U.S. Small Business Administration, the main parts of a business plan include the executive summary, a company description (what makes the company unique), a market analysis (the competition and target demographics), the company's structure, a description of the service or product line, the marketing and sales strategy, financial projections -- plus any additional useful information.

A good business plan is a written description of your business's future, your plan  tells  what you plan to do and how you plan to do it. Now if you jot something down on the back side of a book of matches describing your business strategy that would be considered writing a business plan.

A good business plan is strategic in and of itself. You start at point "A" with your resources and abilities and you want get to point "B" in the future ( usually 3 to 5 years out) at which time your business will have different resources and abilities as well as greater profitability and hopefully increased assets. Then you reset your business plan.

"You asked about competitive strengths": Competitive strengths are limited only by your imagination and innovative thinking. Now if you want to identify your competitive advantages then you have to look in a mirror and be honest about it.  If you know you are not the leader in your business market with  the cheapest prices or the best at what you do; then don't claim to be. However, you may be much better at something else, that's where you begin. You look inside your own company to see what your weaknesses are and identify your strengths. Then you set out to strengthen your weaknesses as you accentuate your strengths to your customers. Start a internal-store survey by asking your customers why they shop with you; what they like or dislike about shopping in your store. You may be very surprised by the answers you get.  

Once you determine what your competitive strengths and advantages are they you can begin to tell your customers and potential customers about it. Of course they will begin to form their own opinions about your strengths. If they believe in what you say and you maintain your promises then that is how they will begin to realize you really are different from  your competition. Remember the old adage, "how do you get to Carnegie Hall? Practice, practice and more practice. You have to continually remind them of why you are better than your competition. However, remember this; "if you don't back-up what you say you can do", then you're yesterdays newspaper if you know what I mean.

Now you can go online and Google .  Hannaford Supermarkets", Whole Foods,  Shaws, or Trader Joe's.  They all tell their customers and potential customers their "competitive strengths". But today they call it Sustainability: Here is the definition of sustainability:

Sustainability could be defined as an ability or capacity of something to be maintained or to sustain itself. It's about taking what we need to live now, without jeopardizing the potential for people in the future to meet their needs. If an activity is said to be sustainable, it should be able to continue forever.

Hope this helps!