I have to echo what others have said and that practice combined with good equipment is your friend. I'm not a full time sly, a lot of the time I will just buzz it as it is faster (however slying it is becoming more common as I do prefer the look). This morning as it is my day off I went for the sly experience and I'd say it took no more than 10 mins. Like I say I'm still learning the skill but I'm guessing maybe having buzzed my head for 10 years now maybe that has developed a technique and muscle memory.
I don't have a fancy routine or fancy equipment. I use a Gillette ProGlide that became redundant when I grew my beard!!
- Fill sink with hot water
- Splash the water on my head and give it a rub
- Foam up my dome (no fancy product just normal shave foam)
- Take the razor and starting at my forehead go back in strokes against the grain (tbh there isn't much up there to cause resistance anymore!)
- I'll then work round the horse shoe going with the grain (this take the most out but I still feel stubble)
- Foam up the dome again and repeat the process but this time going against the grain and this gets me smooth.
- Jump in the shower but keep the razor to hand to sort out the couple of patches I'll have missed (using soap as lube)
- After drying I'll slap on a bit of moisturiser (for the ladies!

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I found that how you hold the razor is key, the ProGlide has a hinged neck to it, I hold it between 2 fingers just before the hinge and having a finger infront of the razor head so I can feel the rough spots and follow them.
Fortunatly I havn't experienced any soreness but I dunno if that is just because my head is hardened to irritation after a decade of buzzing it, but I'd say it'll get better in time!!