Rule 1
If a regular verb ends in -e, add -d to change to the apst and the past participle form.
i.e. like → liked
     decide → decided

Rule 2
If a regular verb ends in consonant + -y, change -y to -ied.
i.e. study → studied
      try → tried

Rule 3
If a regular verb ends in vowel + -y, add -ed.
i.e. play → played
      stay → stayed
Some exceptions to this rule are for example “pay (paid)”, “lay (laid”).  

Rule 4
If a regular verb ends in a consonant + vowel + consonant pattern, double the final consonant and add -ed. 
i.e. hug → hugged
      plan → planned
This rule also applies to regular verbs which stress is in the last syllable.
i.e. prefer → preferred

Rule 5
For all other verbs, add -ed. (Regular verbs that do NOT follow any of the previous rules)
i.e. ask → asked