As you know, you set "parameters" according to what you want to instruct the LCD to do. You can send the LCD either Commands or Characteres. You do that by switching RS. RS of 0 will allow you to send comands, so what ever is on your data pins will be interpreted as commands. Then look at this table enabling or disabling the bits on the D7-D0 will allow you certain things:
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Hope it helps you
Ivancho