For primers 17-25 base pairs, a 4uM concentration is generally adequate. For one sequencing reaction, the total volume of template plus primer may not exceed 12ul. Templates should be diluted so that the concentration does not exceed the maximum recommended concentration in one microliter for the type of template being used. Low template concentration will result in low signal, noisy data, and errors in base calling. High template concentration causes the peaks in sequencing data to become top heavy with strong peaks at the beginning of the run that fade rapidly.
Mixed templates have multiple priming sites causing overlapping sequence peaks.
Overall weak signal results in noisy data. This is related to the tighter duplex and greater difficulty in denaturing the template, as well as the presence of secondary structure. Reduce the annealing temperature of the reaction. Linearize plasmids with a restriction enzyme. Many of the above approaches may improve sequencing data.