Nice! I'm no expert but I've played a fair bit and I love it. There's Italian Spartacus and Party Elite on Youtube who both have some pretty good intro videos to the basic concepts. This guy has great tips, once you figure out the very basics. I found the videos really useful where he rescues peoples save files that have gone horrendously wrong.
My own hot tips. Probably start with the Easy recommended campaigns. There so much, and so much I dont know but anyway..
-Pay attention to the message menu at the top centre, everything important that is happening is listed there.
-If it all goes wrong just go with it and try and work through, hardly anything is the end of the game and finding creative ways around mistakes you've made through ignorance of the rules was a lot of the fun for me.
-Start as a Catholic, if the Pope likes you he'll give you a good chunk of free money every few years.
-Use money to build in your capital first! You can build anywhere, but you'll only get 100% of the benefit from counties in your direct domain. You can lose almost any county through succession when you die, but I believe that your main heir always gets the capital.
-Get allies, marry off your daughters to those with the biggest armies to help scare off any potential attacks or help with invasions.
-Get your player character and main heir married to someone with the genius trait ASAP. Your children are more likely to get an intelligence trait which give bonuses to all stats. Genius is +5 to all.
-Marry your court members to useful characters, with high skills to be councillors, future vassals or high Prowess to knight for you. Try and keep them the same culture as yourself if you want to expand your own cultural influence later, and them not to hate you. Later, I like to give titles to members of my own house as it helps with Reknown.
-Whatever your PC's lifestyle preference, start off with the learning tree and pick up the 35% bonus to scientific discovery trait. Switch to whatever you want after that.
-Educate your heir well. For a guardian, you need someone who has a high number rating in the desired skill, someone who has high learning skill, an Intelligence trait (Genius, Intelligent, Quick) and also a 3 or 4 star education trait in the same skill your heir is training in. Doesnt matter where, look in every realms vassals as long as they dont hate you.
-Make sure the church endorses you by using the sway scheme on your Bishop if required, you need his taxes and troops!
-Sway scheme every one of your powerful vassals until they like you, remember to change as it rolls on again
- Learn about succession, with the basic level the whole of your realm will be divided equally between all male sibling (Mostly if you stay in europe) and go out of your control. This is a large part of the reason research is good, because you can prevent it from happening once your culture researches hereditary rule. Dont be shy about disinheriting, murdering, or if you want to keep your hands clean, sending your unwanted heirs into war by forcing them to Knight for you all the time. If you want to get rid of them.
-Diplomacy tree and skill is really good. It makes everyone like you, which means they provide more tax and levies for your armies and dont scheme against you.
-As well as looking for traits, try to marry someone who has high skills in areas your PC lacks. They can support you and improve your own skills via the drop down menu on the council tab.
-Make sure your spymaster likes you, or you'll get murdered.
Uhhh, sorry I'll stop now. This obviously isnt exhaustive and theres definitely many other ways to play but these all worked for me. Let me know how it goes!