It makes musical sense to set vocal delays to be in time with the track. However, straight delays such as quarter and eighth notes can get easily masked within the track. I usually start with an offbeat delay like three sixteenths which I find tends to naturally find the musical gaps. Then I’ll vary the delay slightly until it feels good. Stereo delays are also useful for movement. A quarter note on one side and three sixteenths on the other bounce off each other nicely. A slap delay can be useful, often sounding like a tight reverb when mixed low. I’ll use 80-90ms for those depending on the speed of the track. I’ll also use very short delays of 10-20ms with a bit of pitch change on each side to add thickness and width.
You may find if you work with the same person a lot you get to know characteristics of their voice. For example, I known an actor who has sibilance at about 11 kHz. So I don’t like to boost her voice in that range. Generally speaking, if a male voice is sibilant it will tend to be in the 3-5k Hz range. If a female voice is sibilant it will tend to be in the 5-8k Hz range. But that’s just a strategy. Don’t follow it like a recipe or you may inadvertently trash a recording of someone’s voice who is sibilant outside of the usual range. Sometimes you can see sibilance on a real-time analyzer, which may help you find it more quickly. But if you sweep through the 3-12k Hz region with a narrow Q and a significant boost, your ears will tell you where the harshness resides. Don’t emphasize it in the name of presence.
When you solo an instrument, a good use for EQ is a highpass (low-cut) filter. Filter out frequencies below the lowest fundamental frequency that the instrument produces. Here’s one way to do that: Start with a highpass filter set to a Q of and a frequency of 40 Hz. While playing the track, gradually raise the filter frequency until the sound starts to thin out, then back off a little. Filtering out the deep lows on each instrument and vocal reduces breath pops, low-frequency leakage, and rumble from traffic and air conditioning.