As suggested by Alejandro, you need to be specific, and his suggestion are valuable.
If you just want to increase the intensity of the bands on the gel you can use 0.5 µg/ml ethidium bromide gels. But this depends on the copies of PCR products.
I have also noticed that the template concentration in your PCR can decrease the yield in some cases based on Taq polymerase. So its better to have a DNA template at concentration of ca. 100ng. In some cases you can use DMSO to get better yields.
As already mentioned the context is essential to find the best solution to your problem. What is the purpose of the PCR experiment you talk about? Diagnosis? Analysis?Cloning? Screening? Do you need to quantify the product? What is the current yield of product per volume of reaction?
I wish you had provided more details and an image of your gel, anyway many factors can effect your problem Get sure about your primers whether they are well designed; Use your current PCR material except primer for different amplification reaction to find out if the problem is relating to primers. if your problem is solved then maybe the incorrect annealing temperature is the problem be sure you are using the optimized tmp you can run a gradient PCR maybe you have to decrease your annealing tmp. or maybe the primer concentration is not the ideal. maybe you will have to use a new pair of primers. if you came to this conclusion that the problem is not because of primers then you can focus on Mg concentration, your template DNA quality and possible inhibitors existence in your reaction.
also ask your friends if they are facing such a problem to check thermal cycler proficiency.
Not to sound like a broken record, but details really are needed in order to solve this problem. Previous suggestions point out a lot of important points, but in the end the cause may be as simple as using a too old stain, or with too low concentration.
When PCR products produce a single band on a gel with a weak signal, you can try reamplifying the PCR. Dilute your PCR product to 10E-3 to 10E-5 (DNase/RNase-free water is fine). Take 5 ul of each dilution (10E-3, 10E-4, and 10E-5) and use as template in a 50 ul PCR reaction using the same primers,reagents, and conditions as before. Sometimes this works, sometimes it doesn't.
I agree with Alejandro Martin. You can also optimize the annealing temperature of your PCR. If you need only a better picture, you can try to run the gel with much more PCR product.
As mentioned before, you could increase the amount of template DNA, or optimize the annealing temperature (do a gradient PCR). You could also increase the number of cycles (usually up to 40), increase the annealing time (max to 1min - I have good results with this)or increase your MgCl to 3 or 3.5 ul for brighter bands.