Did Jesus set Himself at God's right hand, or did someone else do it?
God the Father set Jesus at His own right hand. The context explains that the same power that raised Christ from the dead also seated Him in the heavenlies, and the pronoun usage shows this was done by an outside personage. Jesus did not seat Himself; God raised Him and set Him there.
Les emphasizes the pronoun usage in the passage: "which He wrought in Christ, when He raised Him from the dead, and set Him at His own right hand in the heavenlies." The actor is God the Father, identified earlier in verse 17, and Les notes this is again the triune God at work. He stresses that this was done by an outside personage, not by Jesus Himself. Jesus did not come up and say, "I'll set myself down." Rather, Scripture says God set Him at His own right hand, just as was seen in Hebrews chapter 1.
Which he wrought in Christ, when he raised him from the dead, and set him at his own right hand in the heavenly places,