The easiest and commonly used way is to measure the effectiveness of a marketing strategy is to compare the rate of profits before and after the implementation of the marketing strategy. It's better to keep a monthly record of the revenue generated through the business during the implementation of the strategy, so that it would be easy for you to compare the results in the future for the effectiveness of it.
Conduct customer surveys
Your customers can give you the right opinion as to how successful has been your marketing strategy so far. By asking your customers/clients you can get to know whether the strategy implemented has been able induce the effect it was supposed to, or has it been the other way around.
Is it fulfilling the strategic objectives?
You should make sure that the marketing tactics applied should fall in accordance with the primary goals of the firm. At times it happens that although the market strategy implied is successfully achieving its own objectives, however it might fail to serve the goals of the firm. Moreover, the planned tactics might also fail to create the desired impact, which is also a sign that it's not achieving the expected results.
Compare with your competitors
Compare your marketing strategy with that of your competitors to see which has been more effective. Analyze the technical perspectives of the strategy being implemented including how are they advertising? How are their profits turned out to be after the implementation? Which are the tactics that they have been applying? Keep that in mind that the strategy working for your competitor might not always seem to work you.
Calculate your ROI (Return on Investment)
Another approach for the effectiveness of the strategy is to calculate the Return on Investment (ROI). The main question that needs to be answered is that whether the allotted marketing budget is justifying the large chunk of money being spent through its results. Calculate the total cost of each campaign including the labour (man-hour) cost, and then measure the value generated by the campaign by measuring the cost against benefit ratio.
Don't forget to keep an eye on the strategy implementation
Try to make sure that your strategy is being correctly applied by keeping a close eye on the strategy's implementation. That can be done by setting up criteria to evaluate the progress towards each goal by the end of a specified interval.