What you sketch with, is very important- in fact, this would be one of the main things that will determine whether you’ll keep sketching or not through the years, because what you use to sketch becomes an extension of your sketching hand.
You need to practice with every kind of material you can lay your hands on. Pencil, charcoal, charcoal pencil, ball point pens, felt tips, micro nib pens. Coloured pencils, brush pens etc.
Go to the shops and get a host of these things and just try the out and see which one you are comfortable with.
What you’ll be looking for is something that makes you want to sketch with it more. It’s that flow, that natural affinity to the medium that you are looking out for. Because the reality is: there’s always something that suits each one of us better.