There are some spelling rules for adverbs ending in -ly. They are :

Rule 1

Add -ly to the corresponding adjective. Consider the following example
nice –> nicely
quiet –> quietly
beautiful –> beautifully

Rule 2

If the adjective ends in a consonant + y, change the “y” to “i” before adding -ly. See the following example
easy –> easily

Rule 3

If the adjective ends in -le, drop the “e” and add -y. See example below
possible –> possibly

However,do not drop the “e” for other adjective ending in -e. Except :
extreme –> extremely
true –> truly

Rule 4

If the adjective ends in -ic, add -ally. Look at the example below
basic –> basically
fantastic –> fantastically

Good Luck!