Besides learning whether a German verb is ein starkes verb (irregular verb) or ein schwaches verb (regular verb), transitive or intransitive, here are some spelling generalities to be aware of when you conjugate German verbs.
- Verbs whose stem ends in s, ss,ß, x or z: no s insertion in 2. person singular needed because these verbs already contain an 's' or similar sound.
For Example:
wrong = du mißst correct = du misst (messen = to measure)
wrong = du reisst correct = du reist (reisen = to travel)
- Regular verbs whose stem end in a't' or 'd' : 'e' insertion after the stem end.
For Example:
arbeiten = to work
Present: ich arbeite, du arbeitest, er arbeitet, wir arbeiten, ihr arbeitet, sie arbeiten
reden = to talk
Simple Past: ich redete, du redetest, er redete, wir redeten, ihr redetet, sie redeten
Same rule goes for regular verbs whose stem ends with a consonant (except for l and r)+ m or n
For Example:
wrong = du atmst correct = du atmest (atmen = to breathe)
wrong = ihr ordnt correct = ihr ordnet(ordnen = to organize) - Most irregular verbs with the stem vowels a, au or o in the present 2. and 3. person singular have an umlaut change.
For Example:
schlafen (to sleep)-> du schläfst br> stoßen (to bump)-> er stößt - Many irregular verbs with an e in their stem vowel, is changed to an i in the present 2. an 3. person singular, as well as in the singular imperativ.
For Example:
brechen (to break) -> du brichst
helfen (to help) -> er hilft
geben (to give) -> Gib her!
Source...