I am learning a 8 hole bamboo flute. I am having difficulties in practicing it because I am getting different sounds for different lip positions. Are there any tricks or ways to get the right sound apart from the normal way of practicing it for a long time?
Making some assumptions here: you're talking about a transverse flute whose playing technique is similar to that of a typical C flute.
If by "different sounds" you mean "different pitches", then read below. Otherwise, if you are either getting a good tone or not getting a good tone, that's just going to take practice until you can play a good tone reliably. Here are three techniques for achieving the correct lip position (embouchure): use the one that works best for you (though in concept, they should all get you to the same place):
If you are getting different pitches, the sounds you are hearing are most likely in the harmonic series above whatever fundamental note you are fingering. Your goal should be to practice these so that you can control them. In general, if your airstream is aimed toward the floor at an angle, across the tone hole of the flute, you will get a higher pitch with a more intense airstream aimed at a point on the floor farther away from you.
Practice with a basic note (left hand fingers down, right hand fingers up) by playing up and down in the harmonic series without changing the fingering. Once you are comfortable controlling which pitch you want to hit at what time, you will be able to aim directly for the fundamental note with the fingering that you are intending to play.