别上当

Don't fall for it! 

Fall for 有上当的意思，过去时是fell for，do not fall for it 就是不要上当。

例句：

• Don't fall for that! He is just playing a prank on you.
• 他在拿你恶作剧，别上当。
• That was such an old trick. I cannot believe I actually fell for it. 
• 这是老把戏了，简直不敢相信我居然会上当