Increasing/decreasing signal intensity in Western blotting
There are several different places in a typical Western blotting protocol where conditions can be altered to modulate signal intensity. The first is the amount of protein loaded - more protein will give a stronger signal, less will give a weaker signal. However, too much protein can result in indistinct bands, increased background, lane distortion, and other issues.

The next condition to change is the amount of primary antibody and the incubation buffer. More primary may lead to an increased signal, but too much can give higher background. Some antibodies give a better signal when diluted in BSA, others when diluted in nonfat dry milk. Generally, milk will give you a cleaner blot, but may reduce the signal. Incubation time can also affect specificity and signal intensity - some antibodies will fully bind with a 1-2 hour incubation at room temperature, others require an overnight incubation at 4°C.

The third condition to alter is the amount and type of secondary antibody. Increasing the amount of secondary may increase signal, but again may result in increased background. There are also different types of secondaries, depending on your detection system - HRP for chemiluminescent detection, AP for colorimetric, fluorescent tags for imaging systems, etc. These have different sensitivities, but can also result in increased background, depending on the other conditions of the protocol.

Finally, the type of detection system can affect sensitivity. For example, when using standard HRP-conjugated secondaries, there are numerous different ECL substrates with widely varying sensitivities. Here is a list of different systems available from Thermo/Pierce, ranging from standard ECL to Femto.

So, while Western blotting seems like a fairly straightforward procedure, there are many places to optimize the conditions to get the results you're looking for.