An enclitic retains its accent (is orthotone, cp. cross181 N.):
a. When it is emphatic, as in contrasts: ἢ σοὶ ἢ τῷ πατρί σου
b. ἐστί is written ἔστι at the beginning of a sentence; when it expresses existence or possibility; when it follows οὐκ, μή, εἰ, ὡς, καί, ἀλλά (or ἀλλ'), τοῦτο (or τοῦτ'); and in ἔστιν οἵ
c. In the phrases ποτὲ μὲν . . . ποτὲ δέ, τινὲς μὲν . . . τινὲς δέ.
d. After a word suffering elision: πολλοὶ δ' εἰσίν (for δέ εἰσιν), ταῦτ' ἐστί.
e. When a dissyllabic enclitic follows a paroxytone ( cross183 d).
N. 1.—When they are used as indirect reflexives in Attic prose ( cross1228), the pronouns of the third person οὗ and σφίσι are orthotone, οἷ is generally enclitic, while ἕ is generally orthotone.
N. 2.—After oxytone prepositions and ἕνεκα enclitic pronouns (except τὶς) usually keep their accent (ἐπὶ σοί, not ἐπί σοι; ἕνεκα σοῦ, not ἕνεκά σου; ἕνεκά του, not ἕνεκα τοῦ). ἐμοῦ, ἐμοί, ἐμέ are used after prepositions (except πρός με; and in the drama ἀμφί μοι).
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].