Formal:
* Compliant: willing to obey.
* Docile: easily managed or controlled.
* Submissive: willing to obey orders or submit to another's authority.
* Deferential: showing respect and submission to another person.
* Amenable: willing to accept or be influenced by a suggestion.
Informal:
* Well-behaved: acting in a proper and acceptable way.
* Law-abiding: obeying laws.
* Tractable: easily managed or controlled.
* Pliable: easily influenced or persuaded.
* Meek: quiet, gentle, and easily persuaded.
More specific:
* Ductile: easily shaped or molded.
* Pliant: easily bent or shaped.
* Yielding: giving way to pressure or force.
The best synonym will depend on the context of your sentence.