Before you begin window installation, there are some steps that you should follow.
The jambs should be level with the framing, but not too level. This will make the casing difficult to install, as well as cause the sashes to jam and stick. To avoid this, be sure to use an assistant on the inside to center the window in the opening. Once this is done, the window installation is complete. If necessary, shims should be placed on the lower edge of the opening.
The first step is to unfold the nailing fins on the window. Then, fold them out, setting them into the rough opening. Then, start putting the window frame into the opening. You can then gradually push the window frame into the opening until the nailing fins are flush with the wall. After this step, you should check the windows for leveling and make sure that they are securely attached. This will ensure that the installation is completed correctly.