If your tracks comprise MIDI performances (audio instruments, soft-synths, samplers) along with audio tracks, first render all virtual tracks as audio tracks, or use your sequencer‘s “freeze” function. This eliminates confusion and saves CPU resources. Since DAWs use math to process audio, technically, you should have more than enough headroom to work with, but in reality, you can run out of headroom fairly easily. Set your track and master faders at unity and listen to the tracks as they were recorded. This will give you an idea of relative balances between instruments, and thus a place to start building a mix from. Watch the master fader peak meters for digital overs. These usually take the form of two boxes side-by-side above the stereo master fader turning red. If you see this, leave the master at unity and bring all of the track faders down uniformly until the clipping goes away. We want to maintain the highest signal-to-noise ratio, which results in clarity in the mix. Leaving the meters at just below clipping won’t allow you room for additional processing such as EQ and compression, which tend to add gain. It follows that you should do this step prior to inserting plug-ins.