I have asked this to myself many times, how do I get the best enchantment on my pickaxe? I just have no idea, I have tried getting a good enchant but all I got was efficiency 1 for level 30 enchant
You have to either keep just trying your luck, or you can use books and an anvil. You do this by enchanting multiple books with low level enchants, and then combining them on the anvil to make higher level enchanted books, and applying to your pick that way.
To illustrate I have 3 enchanted books, one with Efficiency 2 and two with Efficiency 1. I can use an anvil to combine the 2 Eff 1 books into an Eff 2 book, then the 2 Eff 2 books into an Eff 3 book, then apply this to my pick.
Unfortunaltey this means you're much less likely to get enchants like Fortune and Silk Touch.
You can use a tool such as Minecraft Enchantment Calculator to make sure you're at the optimum level for certain enchants.