Can you suggest me how to get protein crystal???

I purified my target protein and concentrated to 12mg/ml (pI 6.04). Final purified protein contains 50mM HEPES pH 8.0 and 50mM NaCl. Then the initial screening was done using hanging drop method but no crystal. So 2mM NADP cofactor was added again screen with Hampton (PEG ion, PEG RX, crystal screen, Index) and Molecular dimensions conditions etc. I got precipitate like formation the image was attached below. From this formation what I can do… mean while I increase the protein concentration and did screening for that selected conditions again I got same kind of formations. I am new to protein crystallography kindly suggesting me. And how much concentration is suitable for protein crystallization?? How to find which concentration is enough for our target protein crystallization?? Thanks in advance