EX- is one of the most productive prefixes in English, meaning "out" or "former": EXACT, EXAM, EXAMPLE, EXCEPT, EXIST, EXPECT, EXPERIENCE, EXPERT, EXPLAIN, EXTRA, EXTREME, EXTEND, and EXPLORE. EX- words are particularly valuable in Scrabble because X is worth 8 points.
EXACT (14 pts) and EXPEL (12 pts) are strong 5-letter EX plays. EXHALE (15 pts) and EXOTIC (15 pts) are excellent 6-letter options. EXQUIZ, EXUVIAE, and EXPUNGE are powerful longer EX plays.
High-value word starts for Scrabble, Wordle, and crosswords