For stable strains it is best to start with stabilized strains. Such as a IBL Northern Lights or Brothers Grimm C99 etc. Buying, using and breeding with poly hybrids equals poly results. Read as way to many phenos. Not stable at all. Learn how to select from what you grow and love and start a cubing process from there. After about the 3-4th gen of back cross you should have what you want to keep trait wise in seed form. It takes a long time and lots of selecting and working to fix traits or at least find and work with the dominate traits. Some strains will never be stable because its in their genes or recessive ones anyway. Other stabilize well. Look for IBLs to work with and go from there. Or take a chance and try to cube what you have a male and female from. Robert Connell Clarkes Marijuana Botany is really good though a bit dated. But for most also very technical. Spend lots of time reading all you can until you get the gist of how to do it. Mean while start with what you have.