Learn Swedish: Vi övar uttalet lite oftare än ordförrådet. - We practice the pronunciation a little more often than the vocabulary.

While övar på is very common, especially before verbs (övar på att tala - practice speaking), you can often drop the på when the object is a direct noun representing a skill. Both vi övar uttalet and vi övar på uttalet are correct, but dropping the preposition is very natural and common in this context.

What is the literal meaning of ordförrådet?

It literally translates to the "word supply" or "word store". It is a compound of ett ord (a word) and ett förråd (a supply or storage). Since förråd is an ett word, the definite form takes the -et ending to become ordförrådet (the vocabulary).

Could I say mer ofta instead of oftare?

You would be understood, but oftare is the correct and much more natural choice. In Swedish, short everyday adverbs like ofta take the -re ending for the comparative (oftare) and -st for the superlative (oftast). You generally only use mer (more) for longer, more complex words.

Why use the definite forms uttalet and ordförrådet instead of just uttal and ordförråd?