Help with organic chemistry lab question

You carry out a TLC experiment using toluene as your eluent and the results are unsatisfactory. You then add cyclohexane to the toluene. 

a) Before even considering the ability of the addition of cyclohexane to toluene to differentiate the spots, what criteria must be fulfilled by the mixture of cyclohexane and toluene? 

b) Using the mixture of cyclohexane and toluene as the eluent yields desirable results. From this information, were the developed spots from your sample all toward the bottom or top of the plate when you were using toluene alone? Explain why this undesirable result was observed.