help me on how to start

i'd advise the opposite
do the GMAT first. then TOEFL.
you might want to take your time on the GMAT, you might want to take it more than once... so start early. if you start late you might put yourself under unnecessary pressure.
TOEFL scores are applicable only for 2 years. GMAT for 5. since there might be a possibility that you'll need to postpone your plans one year (you know... things change: you might be happy at your job, you might not get admitted to the school you want, personal circumstances may change etc...). if you start with GMAT, and finish the TOEFL only when you actually start the admission process then you won't risk that you'd need to rewrite the TOEFL.

TOEFL is relatively easy, and expires fast. so do the GMAT first.
that's my advice.