Take Nethravathy or Graibreth train and get down at Thane. Purchase a local ticket to Bandra, take local train towards CSTM and get down at Dadar. From Dadar take Foot over bridge and cross to Western line (Western Railway) and take local train which goes towards Virar/Borivali/Andheri and get down at Bandra.
Second option is get down at LTT last stop and take a rickshaw to Bandra which will cost around Rs100/-
Third option is if you are travelling in the train which passes through Mumbai , that is, the trains...
more... that goes to Gujarath and Rajasthan side get down at Wasai Road and from there take a local train towards Churchgate or Dadar and get down at Bandra.
Fourth option least prefered and a little confusing for first time traveller: get down at last stop LTT go to Thilak Nagar station walkable distance from LTT purchase a local ticket to Bandra and take train towards CSTM (harbour line) get down at the very next station Kurla and take another train towards CSTM (Main line) and get down at Dadar. From there as described above take FOB cross to Western line and take local towards Virar/Borivali/Andheri.
Thank you.