[Grammar] about preposition

[moqaddas]

I have an idea ''let's go for a picnic''.
or
I have got an idea''let's go to a picnic''.

Which is better to say?
and
I am confused about preposition as well,tell me about it.

 

[moqaddas]

Gil

I wanted to ask about ''have'' and ''have got''
and
preposition ''to'' and ''for''?
I have an idea ''let's go to beach''/I have an idea to go to beach.