Will changing things on my page effect my keyword placement on search engines?

have a site that i have had for over 8 years now and have not paid to much attention to it lately since i have been working on other projects. I decided to check today how some random ones were doing and discovered that i am getting a fair amount of traffic to a site a month and i do not have any ads running on the pages that are creating the traffic. Figured i would fix this and ad some ads and start updating the site along with adding a new sitemap to the site since i have over 200 errors of not found pages on there from the last time i updated. Main question is will doing all this stuff hurt my keyword ranking on search engines? i am on the first page for alot of main keywords and do not want to have it screwed up by making these changes. Any Advice?

I would think as long as you have the same amount of kw 's on the page and your titles etc are not changed too much, you'll be fine. Changing title tags and messing with the kw density MIGHT effect things.

Hopefully not. I am not messing with any keywords or any of the writing basically just adding some advertisements and cleaning it up a bit. I am hoping that if i add a completely new sitemap to the site will not hurt it though. Also see that i have not done the best in the past with the page names and some of the pages come up as http:/qqq.sitename.com/title%20title.... i know this is because i added a space in the page name so if i take this out it should only help my ranking right? that specific type of one is on the 3rd page of google so if i change it do you think it will disappear or rank it higher? Appreciate the help btw. I have been sloppy in the past and just trying to get things running smoother

Don't change titles, permalinks, or the content itself. Try monetizing the site with sidebar ads or you could give
Info Links a try. I like ads that focus on user intent and it won't change your actual site layout.

I would change as little as possible; if it ain't broke, don't fix it. Do the minimum you need to do.

IF you don't change the headlines and linking structure; you will be fine

Hello,

Firstly if your website is already on first page then why are you intended to make changes, and if it is necessary than you should make changes of those things which do not affect you keyword ranking in search results pages.

Good Luck!