Noung's writeup elsewhere in this node is great. It is, however, easy for someone new to this activity to confuse strengths with opportunities and weaknesses with threats.

Simply put, Strengths and Weaknesses relate to factors within the organisation's internal environment that can influence it's performance. On the other hand, Opportunities and Threats describe those factors that are external to the organisation.

Examples of factors from the Internal Environment

Sales and performance
Comparision of your pricing policy to industry practices, ability/desire to meet customers needs and wants, market share and level of sales, current market trends, strength of business plans.
Experience and expertise of employees, staff training, motiviation and utilisation, use of external business advisors.
Capital resources
Plant, facilities and equipment.
Financial resources
Effectiveness of systems; cash flow; access to additional funding, financial information and indicators; credit terms, debt collection systems
Potential for growth and improvement.

Examples of factors from the External Environment

The Economy
Current interest rate, position in the business cycle
Quality of product and service, pricing policy, their customer base and relationships, their performance
Innovations, development of substitue products, cost (as a barrier to entry).
Socio-Economics Standing & Demographics
Standard of living, population make-up, age distribution etc
Environmental & Legal
Environmental and statutory regulation, requirements and other issues.
Physical Factors
Climate, public infrastructure