How do I choose which enchantment to accept in Minecraft?

Solution 1:

Enchantment names are randomly constructed from the following list of words. Three to five words are chosen from the list and appended to each other, then displayed in the Standard Galactic Alphabet. Note that the names have no meaning and are not saved on the enchanted item (meaning they will tell you nothing about what the resulting spell will be), and they are only displayed in the Enchantment Table interface.

Source

This might help to decide which one is the best for you. Source

Also you should look at the source, since your level is modified by the tool/material of the tool. And what you get is randomized of the possible enchantment. A few of these enchantment have more "weight" during this randomization, you can find a table for the enchantment weight also on the linked page.

Solution 2:

Ultimately you can't choose - the result of the enchantment is supposed to be random.

It works out various modifiers based on your experience level, the number of bookcases etc and then applies that to the level it will actually apply to the item.

You always get at least one enchantment. The first enchantment is picked from a list of statistical "weights" - the enchantment with the higher weight has a higher chance of being selected.

P(enchantment) = (enchantment weight) / ( ∑i=1^{number of possible enchantments}[enchantment weight_i])

So the effect is random.

For more information on the mechanics of enchantment see the Minecraft Wiki