Bits and bobs:
A large part of drawing well is about observation. If you get people to draw a jug for the first time, you often get something quite accurate for the first two thirds, and then it goes wonky. It's the point they stop actually looking, and imagine the last bit, because we all think we know what it looks like. We do, but not maybe well enough to draw it from memory. 
Hence grid drawing and tracing can be helpful, because it makes people really look, but can have some drawbacks.
Good pencil grip, but most of all constant practice, both in drawing and in observing. Doesn't have to be long sessions, though they never hurt.
When you're drawing, you're often taking a 3D thing, and mentally reducing it to 2D to gain the line, then using light and shade to bring it back to 3D, so if things look flat, the chances are you just haven't quite got/finished the third bit.
Drawing the gap in between objects, people, plants, etc, can teach you a great deal.
Re less general tips: Is there any particular artist whose style resonates with you? and anything in particular you'd like to be able to draw first?