Turkish vocabulary (see Turkish Vocabulary) benefits enormously from understanding that suffixes don't just mark grammar — they actively build new vocabulary from roots you already know.
Treat common derivational suffixes (the ones that turn a verb into a noun, or a noun into an adjective) as vocabulary items in their own right — once you know a handful of these, you can recognize (and sometimes even construct) new words from roots you already have.
When a word feels unusually similar to an Arabic, Persian, or French word you might know, that's not a coincidence — noticing these historical loanword layers (see Turkish Vocabulary) can make certain vocabulary genuinely easier to remember if you have exposure to those languages.
Occasionally pairing a new word with a already-known word of the opposite vowel group reinforces both the vocabulary and the harmony classification at the same time — a small but efficient double-purpose habit.
Some roots appear constantly across many different suffixed forms in everyday speech — learning these thoroughly gives you outsized returns compared to rarer roots that only appear in a couple of contexts.
See also the reference page: Turkish Vocabulary.
Both — derivational suffixes actively build new vocabulary from roots you already know, so learning common suffix meanings expands your effective vocabulary well beyond the words you've directly memorized.
Because of historical loanword layers from centuries of contact — recognizing these connections can make certain vocabulary easier to remember if you already have exposure to those languages.
Occasionally, yes — pairing a new word with an already-known word of the opposite vowel group reinforces both the vocabulary itself and your vowel harmony classification skills at once.
High-frequency roots that appear across many different suffixed forms in everyday speech — these give outsized vocabulary returns compared to rarer, narrowly-used roots.