Yes, PREPARE is a Scrabble word!

Letter values in Scrabble US: P 3, R 1, E 1, P 3, A 1, R 1, E 1.

Is it a valid word?

PREPARE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

make ready or suitable or equip in advance for a particular purpose or for some use, event, etc
prepare for eating by applying heat
to prepare verbally, either for written or spoken delivery
arrange by systematic planning and united effort
educate for a future role or function
create by training and teaching
lead up to and soften by sounding the dissonant note in it as a consonant note in the preceding chord
undergo training or instruction in preparation for a particular role, function, or profession

Also: set up, gear up, get up.