Latvian pronunciation (see Latvian Pronunciation) is unusually rule-governed — which means deliberate practice pays off faster here than in languages with more irregular pronunciation.
Since stress falls on the first syllable in the vast majority of Latvian words, practice reading new words aloud with exaggerated first-syllable emphasis from the very beginning — building the right habit early is much easier than correcting a wrong one later.
Find or create pairs of words that differ only by short vs. long vowel, and practice them back-to-back — this is the single most effective way to train your ear and mouth on a distinction English doesn't require you to make.
Because Latvian spelling maps so consistently to pronunciation, reading aloud is unusually productive practice here — each session directly reinforces both vocabulary and pronunciation at once, more so than in less phonetic languages.
These postalveolar/palatal sounds are distinct from their unmarked counterparts and worth deliberate early practice — see Latvian Alphabet for how they're marked in writing.
See also the reference page: Latvian Pronunciation.
Placing stress on the first syllable — since this applies to the vast majority of Latvian words, building the habit early is far easier than correcting it after it's set.
Practice minimal pairs — words that differ only by a short vs. long vowel — back-to-back, since this is a distinction English doesn't require and needs deliberate ear-training.
Yes — because Latvian spelling maps so consistently to pronunciation, reading aloud reinforces both vocabulary and correct pronunciation simultaneously, more effectively than in less phonetic languages.
Not especially, but they are genuinely distinct sounds from their unmarked counterparts and are worth dedicated early practice rather than assuming they'll pronounce themselves correctly by osmosis.