Could you tell me some important Japanese words I should know
I'm learning Japanese and want to know some words that are used frequently, daily, or on a regular basis.

Question

Could you tell me some important Japanese words I should know 
I'm learning Japanese and want to know some words that are used frequently, daily, or on a regular basis.

Answer

Check some useful Japanese phrases here:

www.learn-hiragana-katakana.com/japanese-phrases/

Answer

挨拶。例えば　こんにちわ　お早うございます　お世話になります　お疲れ様です
じゃね　お休みなさい

Answer

Hmmm... Your quetion is a little way too rough.  depends situations.
if you meet someone, you will use greeting phrases like "Konnichiwa", "Arigatou gozaimasu" and "Sumimasen". These are very common phrases in daily communications.

Answer

Ohayou Gozaimasu, Doumo Arigatou Gozaimasu, Dou Itashimashite..