Learn Croatian: Precijenit ću svoju snagu. - I will overestimate my strength.

The base verb is cijeniti (to value, appreciate, or estimate). Here, the prefix pre- carries the meaning of doing something to excess. Added to cijeniti, it creates precijeniti, meaning 'to overvalue' or 'to overestimate'.

Why is the final 'i' missing from precijenit?

This is a rule for forming the Croatian future tense. When an infinitive ending in -ti comes directly before the future auxiliary (ću, ćeš, će, etc.), you drop the final i in both writing and speech. If the word order were reversed, the i would stay: ja ću precijeniti.

Since 'moju' means 'my', why does the sentence use svoju instead?

Because the subject ('I') and the owner of the strength ('my') are the same person. Whenever the subject owns the object in the sentence, Croatian requires the reflexive possessive pronoun svoj (here conjugated as svoju to match the feminine accusative noun snagu).

Why does the word snaga change to snagu here?

Snaga (strength) is the direct object receiving the action of the verb, so it must be in the accusative case. For feminine nouns ending in -a, the accusative ending is -u.