Use meaning first; do not classify a word merely because it is mansub.
1. Find the verb and its action.
2. Ask: when did it happen, or where did it happen?
3. Identify the noun that supplies that time or place.
4. Decide whether it is an adverb of time or an adverb of place.
Maf'ul bihi, maf'ul mutlaq and maf'ul lahu can also be mansub, so the final vowel alone does not establish the role.