One of the best ways to make your synth sound better is to dedicate a layer of sub frequencies to beefing it up. Provided you take care if you are also mixing bass synths into the song, it can add a nice element to the track. This tip is of particuler use for dance and electronic music where you want plenty of low frequency weight under your main melodies.
There are several ways to get the sub incorporated into the synth, probably the simplest way is to dedicate one of the oscillators to the sub. Simply set a fairly clean waveform and pitch it a few octaves lower than the melody. Ideally this won't be hugely modulated so if your synth has the option of routing various oscillators to filters, even better.
In Massive, the slider on the right of each oscillator
determines what filter the signal is sent to.
Another method is to use a dedicated synth for the sub and just double the MIDI file. This method is good if you want all the oscillators on the main synth dedicated to the sound. It also means you have a bit more flexibility - perhaps you want more unison on the main synth but not on the sub. It also allows you to control the sub as a separate instrument and as a layer. Finally, it allows you to add reverb to the main synth sound without adding it to the sub.This method will work well in a Synth bus with the main synth and a bit of compression to glue them together.
In a similar process to kick layering, adding your sub as
a separate layer allows for more control.
If you are doing the above method, make sure your sub is set to monophonic mode as overlapping bass notes cause havoc with the mix in normal circumstances. if the melody is complex, consider taking a few notes out to simplify the bass line.
Another thing to consider is automating the bass layer/oscillator to decrease in volume during the verses and builds and slam in on the chorus/drops.