This thesis focuses on creating an testing useful methodology for small business with multiproject environment in practice using principles of theory of constraints and potential for improvement. Small firms have their specific characteristics, therefore aplication of any methodology blindly is not appropriate -- it is necessary to adjust chosen methodology to suit needs of small business. For the small business it is ideal to apply theory of improving performance on the basis of improvement potential, which is based on theory of constraints (TOC) and use theory of constraints (as such) as complement. First of all, it is necessary to analyze chosen firm (for this thesis it will be typical firm) then apply methodology for such firm (on the basis of learning common characteristics, that are common to all small firms of this type) and verify the results afterwards. This thesis describes proper procedure that utilizes both potential for improvement (with emphasis on real potential for improvement) and general. The procedure (or let us say methodology) is verified and its effect on effectiveness of small business management is confirmed in. Thesis also focuses on assigning criteria for evaluation of metodology application succesfulness, and on evaluating results of application of this metodology in typical firm (using above mentioned evaluation kriteria).