I used third party tool for creating xml sitemap for google. Tell me, what's the best way to set priority and change frequency. Software usually do this by themselves.
Well, many sitemaps products/services just assign same value to all pages. You can try check this article about priority values. A1 Sitemap Generator weighs all links across the entire website and from there deduce priority of the individual pages.
i think ignoring that priority criteria is better because i'm sure most of the people is assigning 1 to priority and i'm sure google also knows this and they are ignoring priority
If you set all pages to the same value (e.g. 0.5 or 1.0), you are telling Google that all your pages are all equally important. I recommend either: Leave out priority entirely. Set all priority values manually. Have e.g. A1SG calculate priorities.
I use SOFTplus GSiteCrawler and it sets priority for each individual page based on the amount of activity the page receives (impressions). I recommend you use automated software the like one I specified, rather than setting them yourself.