The "rule of thumb" is generally planting annuals after all danger of frost is past in your garden. I'm in southern New England Zone 6a so that would mean planting annuals after mid-May. Perennials aren't generally as susceptible to frost damage as annuals although each plant type is unique as regards its frost hardiness. When in doubt, always err on the side of caution if only for your peace of mind.

I agree with GWeed, and one more suggestion. You said, "seeds for flowers to sprinkle in my garden", but IME if you plant in rows as opposed to randomly, it makes it a lot easier to determine what are weed seedlings and what are flower seedlings if you aren't familiar with the various seedlings.

By planting if you mean sowing the seeds the dates in relationship to the last frost should be on the back of the packet. Some seeds are sown a week or two before last frost while others are sown after last frost. Be sure to loosen up soil and follow directions on whether to cover seeds or just press the them on top of the soil.

Ok thanks so much everyone!