You can use pli directly with adverbs and adjectives.
- pli rapida = faster
- pli longe = for a longer time
When working with amounts, you need da - the preposition for amounts.
- Pli da tempo = a greater amount of time.
- pli da spaco = a greater amount of space.
In certain cases, we can use "more" for both of this situations in English, but that's not how Esperanto works.