Не в свои сани не садись

а) People should not undertake a task they do not know how to do, and they should not speak about matters they are ignorant of See Беда, коли сапожник начнет печь пироги, а кузнец тачать сапоги (Б), Берись за то, к чему ты годен (Б), Ласточка лепит гнезда, пчелка - соты (Л), Не за свое дело не берись (H), Не суйся в ризы, коль не поп (H); b) You must know your place and should not try to equal people superior to you. See Всяк сверчок знай свой шесток (B), Гусь свинье не товарищ (Г), Знай, кошка, свое лукошко (3), Куда конь с копытом, туда и рак с клешней (K), Лезет в волки, а хвост собачий (Л), Сапог с сапогом, лапоть с лаптем (C), С суконным рылом в калачный ряд не суйся (C)

Cf:

a) The cobbler must stick to his last (Br.). Every man as his business lies (to his business, to his craft) (Br.). Every man to his trade (Am., Br.). If you are a cock, crow; if a hen, lay eggs (Am.). Let every man do what he was made for (Br.). Let not the cobbler go beyond his last (Br.). Let the cobbler stick to his last (Am., Br.). A shoemaker should stick to his last (Br.). Shoemaker, stick to your last (to your shoes) (Am.)

b) As a bear has no tail, for a lion he will fail (Br.). Everyone to his equal (Am.). Every sheep with its like (Am.). Geese with geese, and women with women (Br.). Keep to your own kind (Am.). Tigers and deer do not stroll together (Am.)