English is a complicated language. It's rather annoyingly difficult in many respects, and somewhat simplified in others. Many people have difficulty with English spelling. The grammar has its ups and downs, but here is some help.  This series is for those who would like to brush up on or learn about grammar and grammar terminology.

There are two types of Irregular verbs.  There are those which follow a pattern, and there are those which are truely irregular and must be memorized.  Some involve vowel shifts, which history can explain but most people wouldn't understand it today.  Others involve having two verbs forms in the past and then it became one.  The essential and Modal verbs will be discussed later.  These are the ones which have patterns.

The problem with irregular verbs is that you can't tell when it's irregular and when it's not.  Like and Fly and Cry, where the former's past tense Flew/Flown and Cried respectively.  The first is irregular and the second is regular.  You have other such patterns such as Freeze and Sneeze, and Blow and Flow.

• There is the pattern of i-a-u, /ɪ-æ-ə/ which includes ring-rang-rung (as well as sing), swim, sink (drink, shrink,), and begin.  All of these have the shift from i to a to u. 
• Then there is i-o-i /aj-o-ɪ/, This also might involve add an extra consonant to make the perfect as well as adding -en to the end of the verb.  This includes drive-drove-driven, ride,  hide, bite, rise (arise), dive, write,

Some of the others don't follow such patterns.  Some don't change at all in all three cases.  These include let, hurt, burst, and cost, amongst others.  Read looks like it doesn't change in the past (read-read-read), but the other two are pronounced with a different vowel.
Some vowel shifts involve one shift for the past and the other two are the same.  Lead-led-led, find-found-found, hang-hung-hung, stand-stood-stood, as well as a few others.
Some have variations of the -d, -t, or -ed ending.  These usually are the same in both past tenses.  In many cases the vowel shifts as well.  Sleep-slept-slept, hear-heard-heard, say-said-said, lend-lent-lent, build-built-built, lay-laid-laid, send-sent-sent, keep-kept-kept.

There are even more types of irregular verbs, but you'll have to find and memorize them as the come up.