The exact situation is more tricky but in simple words, I am moving all the content of one of my site which gets lot of traffic to another domain and building new site on the older domain. Now I need to make sure that I don't loose too much traffic and rankings. I will surely be directing the links from older pages to newer pages but a complete 301 is not possible. So what I am asking is, How to minimize the loss of serp rankings when you are moving one site to another domain and putting new content on older domain ?
As long as you can do 301 redirect to your most important pages, I think that's what counts. I guess it can't be helped if you can't do it completely, so you'll probably get lower rankings. Email your contacts about the change in domain, so traffic loss can be minimized.
It's not a good thing to do but there's one solution but it's tedious depending on the size of your site. Create the content on your old domain with all new URL's. Then 301 redirect all your old URL's (which will now be 404) to the new domain. So: original.com/original-page.html 301 to new.com/original-page.html This will take care of everything except links pointing to your original.com homepage. There's nothing you can do about that because you will have a new site on it and can't redirect, so all you can do there is place a link on original.com homepage to new.com homepage. Understand?