start with a clean slate

start (off) with a clean slate

 and start (over) with a clean slate
Fig. to start out again afresh; to ignore the past and start over again. I plowed under all last year's flowers so I could start with a clean slate next spring. If I start off with a clean slate, then I'll know exactly what each plant is. When Bob got out of jail, he started over with a clean slate.
See also: clean, slate, start