Dic: jump in with both feet; jump in feet first; jump with both feet into

jump in with both feet (also jump in feet first)

to become involved in something very quickly, often without thinking carefully about it first

• Take time to think things over before you make a decision, don't jump straight in with both feet.

..... Cambridge Idioms Dictionary

jump in with both feet (also jump with both feet into something)

to become involved in something quickly and completely

• When she decides to get involved, she jumps in with both feet.

... Cambridge Dictionary of American Idioms

• So looking at the next couple of months or two, I'm not advising people to jump in with both feet first. .... International Rectifier in the Chips as Stock, Profits Rise by BRINSLEY, JOHN / Los Angeles Business Journal

..... http://idioms.thefreedictionary.com/jump+in+with+both+feet