Need to solve Joomla Duplicate and 404 error page from My webmaster tools

I have Joomla site. I already all on page optimization. And i also index it by Google webmaster tools. When google index my website its show some "HTML Improvements error" . I need to fix it permanently . Here now Duplicate meta descriptions - 19 error Short meta description - 5 Missing title tag - 1 Duplicate title tag - 65 I already make 301 redirection and try to remove it from google webmaster tools by manually. But here remove some page not all. I need a experienced provider who will solve my this problem and will teach me what i have do when i face again same problem. I need to solve it urgent. I will give you my detail when i award you.