This is a metaphor. In order to make a horse work for you, you put a bridle on it. Thus, "to put a bridle on yourself" means discipline yourself to do something. The phrase means, it isn't difficult to discipline yourself to do something, if you know why you're doing it. It also means, you shouldn't take on a duty or responsibility to someone or something, without carefully analyzing why it's important. I would translate as: "Choose your responsibilities carefully".

literalIy it means : it’s not hard to put a bridle on oneself, povided you know what you do it for, that is you can keep all that you do within limits ,but you should know why you do that

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Надеть узду на себя, впрячься — взять на себя обязательство.