Crystal growing is an art and depends on various techniques.

1.Supersaturation 2.Solvent or solvent mixtures 3.Temperatures 4.External addition and felicitation 5.Crystal lattice of substance itself 6.Nucleation 6.Time given for formation of crystals ......

an interesting review is given by MIT reference..(Growing Crystals web.mit.edu/x-ray/cystallize. Another way to supersaturation, frequently the best way to grow quality crystals, is the use of binary solvent systems. You need two liquids that mix well, and your ....................

There are different methods of growing crystals Viz. Solution growth, gel growth,melt growth,etc. Among this gel growth is the best method of growing single crystal with very good external morphology and structure.

Among various techniques of growing crystals, gel growth technique occupies a prominent place owing to its versatility and simplicity. Crystal growth by the gel technique has attracted the attention of numerous researchers, as this technique is comparatively simple and can be set up in a laboratory with simple glass-wares and without any need of sophisticated instruments and high temperature furnaces. Nowadays this method has been employed to grow not only the inorganic crystals but also to grow biological crystals in vitro because of its resemblance with biological environment.

Maybe you want to have a look at our paper, a tutorial about single crystal growth:

https://www.researchgate.net/publication/230751079_Some_thoughts_about_the_single_crystal_growth_of_small_molecules

Article Some thoughts about the single crystal growth of small molecules