劳驾 and 请
láojià and qǐng

劳驾 is a verb-object phrase used in polite greetings. Originally used only in Beijing dialect, it has gradually been adopted by mandarin speakers.

Sometimes it has the same usage as 请.
(1) 劳驾（请）您一下。
(2) 劳驾（请）您把那本书递给我一下。

But in more formal situations, 劳驾 is not used. Syntactically, one usually says: 劳您驾 or 劳驾你…….

Sometimes both 劳驾 and 请 can be used in a sentence.
(3) 劳驾，请问邮局怎么走？

Besides, 请 also means “to invite, to ask someone to do something," e.g. 请人吃饭，请家教 etc. 劳驾 cannot be used in this way.

“劳驾”是动宾短语，用于客套话，表示有礼貌。原来只用于北京地区，现在已经逐渐被普通话所接受。有时候与敬语”请“的用法接近。
但在一些正式场合，不宜用“劳驾”。在句法上，常说“劳您驾”或“劳驾你……”
有时，“劳驾”与“请”在句子中同时出现。
另外，“请”还有请求、邀请、聘请等意义，如“请人吃饭”、“请家教”等，“劳驾”则不能这样用。