Check before you use plugins. These can be jewels for your blog or prove to be a nightmare in opposite case.

1. Do not use plugin which causes 404 error. Use 404 notifier plugin to know about 404 URLs hitting your blog.
2. Do not use plugins from suspected source.
3. Do not use plugin which causes js warning (object expected or var undefined etc) in status bar.
4. Do not use plugin which is heavy and causes more burden for blog.
5. Do not use old versions of plugins. Always confirm that you are using latest plugin compatible with WordPress version you are using.
6. Do not keep extra plugins in your WP-Plugins directory which you are not using at all.
7. Do not use unnecessary plugins for your blog. Plugins increase your blog pages loading time. Just necessary and essential plugins must be with your blog.
8. Do not use such plugin which does not provide uninstall facility, if it uses database. This will Keep your database clean.
9. Do not use plugin which conflicts your css design and scheme.
10. Do not use plugins which are not well supported. A simple check is to see whether specific plugin is available in Plugin Directory of WordPress or not.

Read more in WP-Plugins context