втереться в доверие

см.
[in good with sb]
[make points with sb]
[scrape acquaintance with sb]
[earn brownie points]
ingratiate oneself with sb {showing disapproval} (to try to get someone’s approval by doing or saying things that will please them) — снискать расположение; втереться к кому-л. в доверие

Example: Innocently moving in with Ray and his family, Christie gradually ingratiates herself with them while setting into motion a diabolical plan. (All Movie Guide, Christie's Revenge")

insinuate oneself into sth (to get into a situation or position by behaving in a way that is not sincere)

insinuate oneself into sb's favour — снискать расположение, милость

in one's good books