An investment plan can be beautiful on paper, but unless you put it into effect it won't help your financial security one bit. This brings us to a truth about investing: for every investor who fails to reach a goal because of making "bad" investments, there are several others who fail because they didn't invest at all. They had a plan that called for making systematic investments over a period of time, but somewhere along the line the planned investments were not made. Setting up an automatic investment plan, whereby you authorize funds to be withdrawn from a checking or savings account periodically for the purpose of making pre-determined investments, can be a good way to go. Although some investors may be wary of losing some degree of control over a portion of their income, this can be a way to make sure that you "pay yourself first."
It is particularly important to guard against any tendency to procrastinate with respect to long-term goals, such as retirement. Depending on when you start investing to fund a retirement plan and how long these funds have to accumulate and grow, a delay of one year in starting the investment fund may mean of loss of $100,000 or more.
Like any part of a complete financial plan, your investment plan and priorities can change as circumstances change, or merely with the passage of time. Because of this, an investment plan is not a "do-it-and-it's-done-with" proposition; you'll need to monitor the plan to gain maximum benefit from it.