Learn Spanish (Spain): A fuerza de practicar, domina la nueva habilidad. - By dint of practicing, he masters the new skill.

The phrase a fuerza de translates to 'by dint of', 'through sheer', or 'by means of intense'. It is used to show that a specific outcome is achieved through relentless, repeated effort. Here it is followed by the infinitive practicar, but it can also be followed by a noun, such as a fuerza de voluntad (by sheer willpower).

Could I just use por instead of a fuerza de here?

You could say por practicar, but it changes the nuance. Por simply gives the cause ('because of practicing'), while a fuerza de specifically emphasizes the intense and repetitive effort involved in reaching the goal.

Why is the adjective nueva placed before the noun habilidad?

With the adjective nuevo, placement changes the meaning slightly. Placed before the noun, la nueva habilidad means it is a newly acquired skill for this specific person. If placed after the noun (la habilidad nueva), it tends to refer to something that is brand-new in its very existence.

Why is domina in the present tense? Wouldn't the past tense be more common for an achieved skill?

The present tense domina emphasizes the current, ongoing state of mastery resulting from all that practice. It translates well to 'he now masters' or 'he has mastered'. If the sentence wanted to focus on the exact moment the skill was acquired in the past, it would use the preterite form dominó.