I assume by suggestions you are referring to suggesting new features.
The meta.stackoverflow FAQ states that you can post questions here dealing with (umongst other things), feature requests.
If your question is about:
- Stack Overflow
- Stack Exchange
- Stack Overflow Careers
- Promotions & Advertising
- Support, feature requests, or bug reports for the core
Stack Exchange engine that powers all Stack Exchange websites
So yes, you can post here on meta suggestions you may have that are relevant to Stack Overflow or even the entire Stack Exchange network.
When making a feature request or suggestion, please explain why you think this is a good idea. Saying "I think this would be cool" or "I'd find this useful" is not enough. You'll have to show how your suggestion would benefit the site and it's users as a whole.
Some tips for feature-request posts -
- Mockups help people considering your suggestion to visualize your idea. It leaves no guessing room and avoids misunderstandings.
- Use-cases will help to explain how this new feature would affect the flow of the user experience.
- Thick skin will help you shake off the possible downvotes on your request; Downvotes on meta are slightly different than on the main site. They indicate that someone doesn't agree with your opinion or doesn't want to see your feature request implemented. They don't necessarily mean that there is something wrong with your post. Keep this in mind!
- Remember that people generally don't like changes. They are comfortable with the system in it's current state and might be weary of any possible changes to their favourite Q&A site. Be careful when criticizing existing features; You don't want people to disagree with you simply because of the tone of your post.