Hi Yusaku,
I think to have a break a good idea.
→I think it a good idea to have a break.
Your sentence should be: I think it is a good idea to have a break.
We need a linking verb "is" to link the pronoun "it" to your opinion (a good idea to have a break).
Very often, we use a linking verb after a pronoun to provide more information about the pronoun.
Example: He IS a man of principle. / They HAVE a lot of experience. / It WILL remain here.
Your experiences make for you to do the job easy.
→Your experiences make it easy for you to do the job.
Your sentence is fine.
Hope this helps.
Cheers,
Lance