It really depends on what you are planning to do with the cells. There are many protocols to prepare competent cells using CaCl2 that work pretty well for general purposes. You can also try electroporation methods. For specific projects that require highly competent cells, sometimes it's better to order those cells from companies to make sure you get the highly competent cells. This can sometimes help you to save some resources especially if you have only one shot.

Look for the Paper from Inoue, H. et al. (1990) Gene 96 23-28. If you can't get it, I can also send you our protocol which is based on the paper.

Thanks for the help.kindly send me the protocol which you used for getting good results.

@Nazia: I attached it here.

thanks Christian Praetorius.