The three-mistake high rule applies here, and try to be at approach speed when trimming!! But there is NO set rule for predicting whether up or down elevator trim may be required-just do as the man says. On a Heinkle bipe, lowered flaps requires up elevator trim; low wing war birds generally require down elevator trim to counter the added lift due to flap deflection-do like the big planes do-fly and find out.
hookemut