This basic reaction setup e.g. for Grignard reaction consists of a three-necked flask, a addition funnel (on the right), a reflux condenser and a gas adapter (for air sensitive reactions). Here are a few pointers for the setup:

1. The entire setup is clamped at the center neck of the three-necked flask. It holds the weight of the entire setup and you can remove the heating source without the flask dropping on the bench. For bigger setups it might be a good idea to support the setup by clamping the condenser loosely in the middle as well.

2.The flask should be not more than half filled to allow enough room for expansion and boiling. Keep in mind that the volume can significantly increase if you add a solution from the additional funnel.

3. The reflux condenser is usually placed in the center. This makes it easier to balance the entire setup. The inlet of the water is on the lower end of the condenser, the outlet at the upper end independent if the condenser is used for reflux or distillation. This way you will get away with a lower water flow for cooling, because the outer jacket of the condenser will fill up with water first before it reaches the outlet. The gas adapter has to be placed on top of the reflux condenser and is connected to the Schlenk line.

4. Make sure that the stopcock of the additional funnel does not leak. It is pretty annoying to start over because you discover that the stopcock leaks after you prepared (flame-dried) the glassware already.

5. The green plastic clips serve the purpose to hold the different pieces of glassware together. They give some more security, but they are not able to prevent the setup from being disassembled if you build up a significant overpressure.

6. If you heat a system, you need to have an 'overpressure valve' somewhere in your setup. It doesn't matter what you heat, the media always will expand (more or less) and will ultimatively build up a significant pressure, which can cause heavy explosions. In many cases, you will connect it to the inert gas part of your Schlenk line. Make sure that you open it before you start heating.

7. Lastly, don't forget to add a spin bar into your flask to mix the solution during the reaction/reflux. Why?