Verbs - past (regular)

For regular verbs, the past tense has two possibilities:de(n) or te(n) behind the ik-form of the present tense. You have to take -te for singular and-ten for plural if this form ends on a k, f, s, ch,p, t or x. To remember this, I use the word kofschiptaxi, containing all these consonants. If the ik-form does not end on one of those, you take-de for singular and -den for plural. So for the verb fietsen, having an ik-form that ends on s, which is one of the consonants in kofschiptaxi, it will be:

    singular                  plural
1 - ik fietste                wij fietsten
2 - jij fietste               jullie fietsten     
3 - hij/zij fietste           zij fietsten

And for the verb rennen (to run), not having an ik-form that ends on one of the consonants in kofschiptaxi, it will be:

    singular                  plural
1 - ik rende                  wij renden
2 - jij rende                 jullie renden       
3 - hij/zij rende             zij renden

Two remarks on all that:

1. Sometimes you get double t or double d where this looks quite weird even to native speakers. The present forms ik antwoord - wij antwoorden (I/we reply)for example, will be in the past tense ik antwoordde- wij antwoordden, and the past of ik plant -wij planten (I/we plant) becomes 'ik plantte -wij plantten'.
2. Where infinitive forms have a v or z that becomes f or s in the ik-form, you must still think of the original v en z when you choose between -te(n) or -de(n). And since v and z are not in kofschiptaxi you get-de(n).