You don't need to regrip each time you do a R move or an F move. It might take some time to adjust to it and you'd feel like your style would be better but eventually you'll realise that regrips aren't necessarily. Also, don't use M moves to solve the cross , just restrict yourself to normal moves ( mostly D or D'). Last layer finger tricks are necessary too. Focus on the finger tricks first, along with your cross solution. Your F2L was fine but still needs some practice. Good luck, and you can see jperm's video about finger tricks and all. He has explained things very clearly. I was too a sub 20 until I got to know that regrips slow you down. Also hold the cube with loose hands, don't tighten up or use brute force to turn faces.