Most Croatian verbs are regular and easy (enough) to conjugate. The only tenses we (really) need to worry about are the present, past, future and conditional.
There are three main patterns of Croatian verb. The category to which the verb belongs, depends on the vowel i,a,e, coming before the ending.
dolazIti:dolazim, dolaziš, dolazi, dolazimo, dolazite, dolaze
gledAti:gledam, gledaš, gleda, gledamo, gledate, gledaju
razumijEti:razumijem, razumiješ, razumije, razumijemo, razumijete, razumiju
The vowel isn't always obvious unless you know the I or ja form of the verb.
And so, it is helpful (crucual) to learn the ja form along with the infinitive.
E.g. vidjeti (to see) with vidim (I see), where it is only from vidim that we can know that the verb is conjugated with the vowel i.
Vidim, vidiš, vidi, vidimo, vidite, vide
Similarly with ići (to go) and idem (I go).
ići:idem, ideš, ide, idemo, idete, idu
A few examples of common verbs conjugated in the present.
voziti. vozim, voziš, vozi, vozimo, vozite, voze to drive
voziti. vozim, voziš, vozi, vozimo, vozite, voze to drive
These are the key irregular verbs
htjeti to go
hoću, hoćeš, hoće, hoćemo, hoćete, hoće
moći can, be able
mogu, možeš, može, možemo, možete, mogu
Remember that the short form of the verb to be can not start a sentence, and so these examples start with čitao. They could have equally been written Ja sam čitao, ti si čitao etc
Čitao sam I read
Čitao si You read
Čitao je He read
Čitala je She read
Čitali smo We read (male)
Čitali smo We read (female)
Čitali ste You read (male plural)
Čitale ste You read (female plural)
Čitali su They read (male)
Čitale su They read (female)
The participle čitao acts like an adjective, where the endings change depending on the gender or whether the noun is singular or plural.
The participle is formed by removing the -ti from the infinitve an adding o (or one of the other endings la, li, le as required).
There are not many irregulars and the common ones that spring to mind are:
ići: išao (to go)
Išao sam u Francusku (I went to France)
Išli smo u pub (We went to the pub)
moći: mogao (to be able)
reći: rekao (to go)
Rekao sam prijateljima (I told friends)
The particple (as used in the past tense) follows these forms of biti.
bih, bi, bi, bismo, biste, bi