well there are not many taboos in conlanging; however, I personally want to see more conlangs with the following features:
- using word orders other than SVO as the basic word order, or using SVO basic word order with mostly postpositions instead of prepositions.
- a priori conlangs without /m/ in base or suppletive forms of 1st person singular.
- a posterior conlangs without generalizing the nominative form of personal pronouns(when generalization happens it is the accusative or oblique form that is more likely to be generalized e.g. modern English you is the generalization of the original 2nd plural oblique form; /mi/ as 1st singular in creoles arose from the generalization of the accusative or oblique forms of English and Romance 1st singular pronouns)
- numerals with irregularities(e.g. 11 and 12 in English) or suppletions(e.g. the -teen and -ty suffixes in English) in respect of the numeral base.
- using strategies other than having a verb meaning "to have" for
predicative possessions
- having
indefinite pronouns derived from interrogatives or generic nouns.
- having some similarities between
universal quantifiers and conjunctions.
- having productive reduplications, either full or partial reduplications.
- smaller phonemic inventory
- the non-use of "th" sounds
-
head-marking in clauses
-
evidentiality
- words indicating some kinds of abstract ideas like cultural values that can't be neatly translated into English or the mother tongue of the speaker
you don't need to do them, though, it is not a sin if you don't want to do these.