Yes easy labs are the hardest score-wise. They're a pain.

-- if you see a destiny near a repeat, always hit that destiny. If it's -4, then it's -4. If it's +4 it's +8 (repeat by whipping around in 3).
-- to me it seems as though Labs are either really good, or really bad, and only occasionally in-between.
-- if you see a large cluster of repeat3s, check your change tile. if it's a +4 you're hooked up.
-- avoid cornering yourself into a destiny. It could be a Block.
-- if you're at the last tile and have over 590 score (but not close to 650), check your changes and hope for a double. 590 + 10 (double tile) +100 (boss x2) = 700.