遊びたいならちゃんとルールを決めておきなさい。

to play; to enjoy oneself; to have a good time; to mess about (with alcohol, gambling, philandery, etc.); to be idle; to do nothing; to be unused; to go to (for pleasure or for study); to intentionally throw a ball to lower the batter's concentration

be; is; indicates past or completed action; indicates light imperative

diligently; seriously; earnestly; reliably; steadily; legitimately; perfectly; properly; exactly; orderly; punctually; regularly; sufficiently; satisfactorily; quickly

rule

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to decide; to choose; to determine; to make up one's mind; to resolve; to set one's heart on; to settle; to arrange; to set; to appoint; to fix; to clinch (a victory); to decide (the outcome of a match); to persist in doing; to go through with; to always do; to have made a habit of; to take for granted; to assume; to dress up; to dress to kill; to dress to the nines; to carry out successfully (a move in sports, a pose in dance, etc.); to succeed in doing; to immobilize with a double-arm lock (in sumo, judo, etc.); to eat or drink something; to take illegal drugs

to do