Four stage model:
 1. Understand the problem
 2. Devise a plan for solving it.
 3. Carry out your plan.
 4. Look back to examine the solution.

     P   I   E   Plan  Implement  Evaluate

Strategies
1.  Act It Out
2.  Make a Drawing or Diagram
3.  Look for a Pattern
4.  Construct a Table
5.  Account Systematically for All Possibilities
6.  Guess and Check
7.  Work Backward
8.  Identify Wanted, Given, and Needed Information
9.  Write an Open Sentence
10. Solve a Simpler or Similar Problem
11. Change Your Point of View
 

When planning, include problems with these characteristics:

Problems that contain superfluous or insufficient information:
    There are 28 students in the class, 15 boys and 13 girls.  3 are absent.
    Why are the worst behaved  children never absent?

Problems that involve estimation:
    How long will it take me to memorize 7 problem solving strategies?

Problems that require students to make choices about the degree of accuracy
 required:
    How many points do I need to earn  a B+ in the class?

Problems that involve practical applications of mathematics to consumer or
 business situations:
    After buying 3 textbooks, will I still have enough money for dinner?

Problems that require students to conceptualize very large or very small
 numbers:
    How many words in textbooks will I have to read to earn my degree?

Problems that are based on students’ interests or events in their environment
 or can be personalized by adding students’ names:
    How late can I leave my house and still get to class 5 minutes early?

Problems that involve logic, reasoning, testing of conjectures, and
 reasonableness of information:
    If the average grade is 88%, and half the students earned an A, what were
        the scores of  the other 12 students?

Problems that have no mathematical answer (but seem to):
    There are 25 students in the class whose average age is 27 years old.
        How many have already taught?

Problems that are multistep or require the use of more than one strategy to
 attain the solution:
    If the students work in pairs to present a problem and each presentation is 7 minutes,
        how long will it take for every student to present?

Problems requiring decision making as a result of the outcome.
    I have $6.00.  Where am I going to eat dinner tonight?