I'll make some random comments because it’s difficult to pinpoint without hearing your tunes.
The bass and kick rule under 100Hz this is their space. Learn it, use it.
The main vocal is the mix, all else should come around it or be built from an arrangement perspective around it. Unless of course you’re doing instrumentals. This range of the human voice is all over the map and you have to adjust the mix around this.
Many modern engineers double track the vocal or at least make at least one or more copies of it and process it separately. Following is an exaggeration but roughly one copy gets compression, maybe twice, one gets delay, one gets reverb, another set up is for other special effects. Then these are combined together on separate busses and mixed back in with the untainted version. This builds a thick and focused version of the key vocal.
Bkgrd vocals are generally recorded with a different and more neutral, sometimes high end focused mic. These are compressed a little more than the vocal to get them to gel or sometimes not compressed at all and used as high freq colors left and right in the mix. Disclaimer: these are not hard and fast rules but generalities.
Once the kick & bass, then the vocals, are cemented in the mix, comes the difficult task of placing those instruments that are going to conflict with the voice i.e. snares, guitars, and pianos come to mind. These have to work around the voice or be placed back in the mix (via reverb or delay or pan) so they are not competing for the key vocal range. Another important tool is volume control, just turn down the guitars or piano when the vocal comes in.
One tool you can use for instruments is to create their own ambience i.e. varying degrees of delay or reverb, short delays or short slapbacks for different instruments. Each instrument having its own delayed sound. When combined it has the effect of creating a room sound that the band has. Lay the vocal on top of this and it tends to glue pretty well. If not, then put some ambience on the vocal to match or counterbalance the instruments.
That's some general thoughts and approaches. Hopefully that will provide some ideas for gluing the vocal in the mix.
