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The simplest thing you can do to make a processor faster is to have faster memory. Usually this means bigger caches or wider memory buses.

You can decode more instructions at the same time. In theory there is no limit to how many instructions you can decode at once.

Those decoded instructions end up in a buffer and execution units can process them if there are no data dependencies. You can add as many execution units as you like if there is enough work for them.

You can avoid performance destroying events like pipeline stalls by predicting the execution flow of instructions. Better branch prediction means less performance is lost.

None of these have anything to do with clock speed.