Literally use hundreds of handouts
Roll20's storage limit is quite big and you should use it. Furthermore the cataloging system allows you to easily group everything, so no one gets lost. The possibility to allow only certain players to see something is very useful.
For the second time I ran a one-shot adventure, about 20 documents, that could be found in various places. The players were as uexperienced as previous group, but they had way more fun. Especially when a dwarf knight found a hidden message, that could be only seen by "eyes, that pierce the deepest darkness".
Avoid splitting the party
I have been using roll20 since June 2016 and played nearly 2 thousand hours with a dozen or so different people, as well as a player and a game master. I know a little about both points of view.
The most important thing, I learned is that spliting the party and player characters may be used by more experienced game masters in classic sit-by-table roleplaying, it definitely should be avoided.
Luckily you use video communicators, so websurfing probably will not happen as it would be too noticeable. However if it happens, make sure to reprimand them. Such behaviour is not only rude, but it also ruins fun for themselves and you as well.
During a real-life game other players may directly give you a subtle hint or two they are getting bored. Unfortunately it is impossible with a camera which lets you to look only in one direction.
If you notice, that spliting the party is unavoidable or the players want to do so you should stop your game at that moment and run a solo-games for every character or group who decided to stick together. It requires more work, but believe not every player wants to wait an hour when their wizard can't solve a puzzle.
Acting and gesturing
Making faces in front of a camera might seem silly, but it really helps. Of course the camera limits your acting possibilities, but nothing stands in your way to perform with your face. If you roleplay someone prudish, raise your head, chin and look not directly into, but under the camera. If it would be some coward slouch, bow your head and look a bit over the camera. Record yourself performing this way and see which facial expressions would fit your NPCs.
Props add a nice flavour
Nothing stops you from using a few simple props. Put on a monocle when you roleplay a rich gnome aristocrat or an owner of a pawnshop. Play with a knife for a dangerous thief. Put on a hood a deep hood for some mysterious people. Drink water from an empty bottle(playing drunk is not recommended) for some drunkard. When they encounter an assassin, pretend you dropped something, bow and put on a mask, that you put under your feet. Slowly stand up and when your face is about to be seen, quickly raise your head. At least goosbumps are granted.
A few regular tips for Game Mastering
Always try to improve your vocabulary. Adding some exquisit words will absolutely improve the game mood. A cutthroat yelling "I will slaughter you one by one." sounds way more terryfying than simple "I will kill you all". Avoid some specialised jargon and be sure you are understandable. Not everybody knows what is Erlenmeyer flask.
Remember to modulate your voice to match. A venerable librarian shouldn't sound like a stalwart army general, just as dragon shouldn't resemble a cute little princess. Use more quiet and calm voice for women and children. For more devillish creatures try to growl, like the singers of heavy metal bands.