The key to riding more confidently in the wet is to.... ride in the wet!
The key points to remember are
If it has just rained (after a dry spell) the road will be slippery so take care. Go easy on acceleration and braking.
Roundabouts are notorious for being slippery in the wet.
Any junction near a petrol station will also be dodgy.
If it has rained for more than one day the roads will be cleaner but still take extra care at roundabouts.
Roundabouts, manhole covers, leaves, potholes, drunk people lying in the road, all things to keep you alert.
I often wonder if riding a bike is some sort of shitty challenge derived by some twisted bastard to see if you can survive the day?
As said, riding in the wet can only be properly mastered by riding in it. Watch any pizza delivery rider lean a bike over in shite conditions. Yes, i agree they're ever so slightly mad, and naive, but it's all about the hours spent on the road.
And again as mentioned, either after a good 2 or 3hrs downfall, or the next day, the rain does really clean the roads, so even though the roads are wet you will feel better grip. It's when it doesn't rain, and you get cold nights, like now, that the roads become hazardous, but you will get the feel for all that after a few years riding.
Add the obvious to the equation though, good reliable tyres. Don't scrimp on tyres (or brake pads), they are your life line. I ride all year round as much as i can and good tyres that perform in the wet are a must for me. If you think you can save £40 or £50 by purchasing cheap tyres then you are being misled and will regret it, because your confidence in riding will go rapidly downhill. Add to that they'll wear quicker, unevenly, etc, so it becomes an issue all round.
Good reliable tyres, common sense and experience will make biking in the rain as pleasant as it can get.
Don't forget the Vee Wipe too, an invaluable piece of kit i simply can't do without!
https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313.TR1.TRC0.A0.H0.Xvee+wipe.TRS0&_nkw=vee+wipe&_sacat=0