Dear Shewa 

May be this could be useful

Article Isolation and Identification of Microorganisms from Crude oi...

Hi Anwar

I think this sequential guideline may help you:

1. Mix one gram of soil sample into 9 ml of diluent (which may be normal saline, phosphate buffer, peptone water etc).

2. Agitate thoroughly to disperse the sample.

3. Collect the liquid portion and carry out serial dilutions with it.

4. Depending on the target species for isolation, you can plate out the diluted sample into a general purpose medium, selective or differential medium.

5. After incubation, distinct colonies are sub-cultured in order to further purify them. They can then be used for further studies.

My regards

Dear Anwar

Greetings

I agree with Mr. Eke  answers ...u can use dilution method for isolation .

good luck