Mixing isn't a formula to identically apply to every song. Each song needs something different. And each source sound is starting from a different place.
The basic tools people use when mixing vocals are compression, EQ, reverb, and delay. If you don't know how to use these comfortably, experiment until you do. YouTube videos may help. Doubling can also help thicken vocals, so consider it next time you're recording.
If you don't know where to begin, start by trying to replicate the vocal sound in a song you like. When you're listening to the professionally mixed song, is the vocal crisper than yours? If so, boost the highs of your vocal with EQ. Is the vocal more forward, and does it have less volume variation than yours? Try compression. Does the vocal sound like it is in a room or space? Try adding reverb. Etc.
If you can reverse-engineer how a vocal sounds in a song, you just reverse-engineered what it would take to get your vocal recording to sound like the pro song you love listening to. Learn, practice, and then get creative.