Those are two
incredibly vague questions. The Neutral game is way too complicated of a concept for anyone to explain it so briefly, and it's also not something you can simply "get good" at. You cannot
practice your Neutral game, you practice a bunch of different things that
form your own Neutral game that is effective in different ways to the situations you are up against. In a way, this comes with matchups studies, matchup experiences, knowing your character well, and recognizing predictable situations at the neutral game, and knowing what to do in them. Basically: pressing the right buttons at the right time.
If you want to "improve at the neutral", the closest thing you can do is learning your character inside and out and then studying whatever MU you'll be up against. This is very far from the only thing Neutral encompasses, but it's a start. You don't go to the gym on your first day and lift 80KG.
You could watch this video and it could help diagnose some of your issues:
Now your second question: It depends. You need to find a way to mix up how you fall to the ground after you started getting juggled. Do double jumps, airdodge unpredictably, use moves that stall you in the air, or if you have the frame data or hitboxes for it, throw a move at them. This is hard. It varies from situation from situation, character to character and person to person.