In any key, there are two adjacent keys to work with; The subdominant and the dominant. Let's assume that we are in a major key. Modulation to the subdominant is easy. The leading tone is a vital part of the key, and flattening it to turn a tonic into a dominant 7th in the new key is extremely effective to modulate to the subdominant. It works immediately.
Modulation to the dominant is much harder. To sharpen the subdominant(which is not a tone in either chord I or V) is nowhere near as effective as changing the leading tone. Even if we use a V(7) in the desired key as a pivot chord, it still sounds like a V(7)-V rather than the primary dominant. I have tried the common idea to cadence in the new key, but even after a couple echo cadences, the dominant function of the supposed new tonic still dominates(no pun intended). It almost seems easier to move through every possible subdominant, eventually reaching our desired key. I'm aware of breakaway and pivot chords, but they always sound like secondary dominants.
How is dominant modulation achieved?