Turn up the master fader
Increase the volume of individual tracks
Reduce unnecessary low frequencies with EQ
Control peaks with compression
Use saturation to add perceived loudness
Limit the master bus to raise overall level
Remove clipping on channels and buses
Balance the mix so no single element dominates
Use parallel compression on drums
Add harmonic excitement with distortion or exciter plugins
Cut muddy frequencies to create more headroom
Keep kick and bass under control
Check phase alignment on layered sounds
Use automation to raise important sections
Reference against louder tracks
Export at the highest practical bit depth and sample rate
Leave enough headroom before mastering
Avoid overcompressing the mix
Use a clipper before the limiter if needed
Monitor at a consistent level while mixing