The main reason you're in school is to earn your degree. Picking good courses at the right time, and in the right order, is therefore critical to your success.
Talk to your adviser
No matter how big or small your school is, you should have an adviser who helps make sure you are on track to earning your degree. Check in with them, no matter how sure you are about your choices. Not only does your adviser most likely need to sign off on your selections, but he or she can also help alert you to things you may not even have considered.
Make sure your schedule has balance
Don't set yourself up for failure by thinking you can handle more courses than you usually take, all with labs and heavy workloads. Make sure your schedule has some balance: varying levels of difficulty, varying subject matters (when possible) so you aren't using one part of your brain 24 hours a day, varying due dates for major projects and exams. Each course may be fine in and of itself, but when combined into a killer schedule they all may turn out to be a big mistake.
Think about your learning style
Do you learn better in the morning? In the afternoon? Do you learn better in a huge classroom, or in a smaller section setting? See what options you can find within a department our course section and pick something that matches best with your learning style.
Aim to pick strong professors
Do you know you absolutely love a certain professor in your department? If so, see if you can take a course with him or her this semester, or if it would be wiser to wait until a later time. If you've found a professor with whom you intellectually click, taking another class from him or her can help you get to know him or her better and possibly lead to other things, like research opportunities and letters of recommendation. If you're unfamiliar with professors on campus but know that you learn best from a professor who engages a class (instead of one who only lectures), ask around and check online to see what experience other students have had with various professors and their teaching styles.
Consider your work schedule and other commitments
Do you know that you absolutely must have an on-campus job? Do you need an internship for your major? If so, will it require you to work days? Consider taking a class or two that meets in the evenings. Do you know you work best when you can plop yourself down in the library for eight hours straight? Try to avoid taking classes on Friday so that you can use it as a work day. Planning around your known commitments can help reduce your stress level once the semester is moving ahead at full-steam.