Open your DAW and begin to create a song template. Label each track with the instruments that you use the most or the ones you think you'll use. Make at least two tracks for each instrument, preferably three or four.
Color-code the tracks by instrument so you'll begin to know by sight what kind of track it is. Your DAW should have a way to put multiple similar tracks in a track folder you can collapse and expand as needed to work on different sections of the song. If there are certain software instruments you use regularly, load them as part of the template also. Save the template.
Document the time, date, and other details about each specific track. You can do this in a notepad-like window that's part of the DAW. If you don't have that, just open up a notepad or spreadsheet separately. Notate when you change things during the creative process. That way of you'll have a record of how to recreate the song if (God forbid) anything ever happened to the song file.
Lay down the foundational track. If this is any kind of modern music (pop, hip hop, rock, etc.), this will probably be the drums. However, some songs work better if you play the melody first and work around that. Whichever method you choose, it will be the foundation on which everything else will rest with the bass line following close behind.
Work in sections, usually four to eight bars at a time. Layer each instrument separately until you have what you want. The best way to do it is to set a section to loop so you can play along live. Then you'll get a sense of what instruments need to be added. Keep adding in this way until the song is complete.