BRP is very intuitive and not difficult to understand. The resistance table is helpful when doing stat checks. The nice thing about BRP is that it give you, the GM/Keeper a lot of Flexibility in deciding what skills to check. I'd say for your first few games, stay away from the more specialized mechanics (drowning, hit zones etc) and stick with the bare minimum mechanics and build up from there as you grow more comfortable and familiar with the rules.
Also, since it sounds like you aren't entirely familiar with the game, I'd say go for a pre-written story. You can construct your own scenarios when you're more used to the general "form" of BRP. Be aware that CoC is very prone to railroading as it is a more story based atmospheric game. HOWEVER, just because the stories are less open do not have the ability to solve the mystery based on a single one shot skill check. Mystery solving is no fun if the case goes cold. Also, get a feel for how "numbers" oriented your group is. If they like rolling a skill check for every. little. thing. Let them. If not, you can try to streamline skill checks for simpler things and save them for when a more unusual situation is happening (time pressure, hiding, or just outside pressure to perform and when failure has a tangible effect. Not just 'I failed a Library Use check' when the character is under no time limit or hurry. Instead if they fail, double the time required to find the document they want, this is more important in early games where everyone is still trying to get a feel for how it works)
Hope this helps
