From H. W. Smyth, Greek Grammar, I §§149-188
GENERAL PRINCIPLES, ANASTROPHE, CHANGE OF ACCENT IN DECLENSION, INFLECTION AND COMPOSITION, PROCLITICS, ENCLITICS
184. Since an enclitic, on losing its accent, forms a part of the preceding word, the writing ἄνθρωπος τις would violate the rule that no word can be accented on a syllable before the antepenult. A paroxytone receives no additional accent in order that two successive syllables may not have the acute (not φίλός ἐστιν).
185. When several enclitics occur in succession, each receives an accent from the following, only the last having no accent: εἴ πού τίς τινα ἴδοι ἐχθρόν if ever any one saw an enemy anywhere.
186. Sometimes an enclitic unites with a preceding word to form a compound (cp. Lat. -que, -ve), which is accented as if the enclitic were still a separate word. Thus, οὔτε (not οὖτε), ὥστε, εἴτε, καίτοι, οὗτινος, ᾧτινι, ὧντινων; usually περ (ἕσπερ); and the inseparable -δε in ὅδε, τούσδε, οἴκαδε; and -θε and -χι in εἴθε (poetic αἴθε), ναίχι. οὔτε, ᾧτινι, etc., are not real exceptions to the rules of accent.
a. οἷός τε able is sometimes written οἷόστε. οὐκ οὖν is usually written οὔκουν not therefore, and not therefore? in distinction from οὐκοῦν therefore. ἐγώ γε and ἐμοί γε may become ἔγωγε, ἔμοιγε.
187. An enclitic retains its accent (is orthotone):
a. When it is emphatic, as in contrasts: ἢ σοὶ ἢ τῷ πατρί σου either to you or to your father (ἐμοῦ, ἐμοί, ἐμέ are emphatic: εἰπὲ καὶ ἐμοί tell me too), and at the beginning of a sentence or clause: φημὶ γάρ I say in fact.
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 some, ἔστιν ὅτε sometimes. Thus, εἰ ἔστιν οὕτως if it is so, τοῦτο δ' ἔστι that which exists.
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.
Reference address : https://www.ellopos.net/elpenor/lessons/greek-accentuation.asp?pg=11