Be sure to keep a dictionary by your side.

Literal

Certainly dictionary [object-を] own beside [at-に] placing [command-起きなさい].

辞書を自分の横に置いて起きなさい — 置いておく means 'to place and leave.' This uses the contracted form 置いておきなさい → 置いて起きなさい. A study instruction about having reference materials ready.