I would say cheat rolls, but only to make does appear more daunting and so players don't get killed so quickly. Knocking them out is not good early on in battle because it means more death saves. That also means players can lose their character quickly. But try not to cheat rolls to have them hover at 3hp for the entire encounter.
Next thing, PLAN FAR AHEAD. Like write down and plan out your first few encounters and have one ready for the next one. This keeps it at a brisk pace that keeps less waiting involved and keeps the party's attention. don't do like my 5e DM and have nothing prepared when he wants to start an encounter and take almost a week to prepare it.
Third, know your players thouroughly. From alignments and stats to the smallest detail in their backstory. This will help you know the characters and give you ideas for quest hooks. It also tells you when you can call a player out on something they should/shouldn't do (such as feel wary around X or Y)
Fourth, don't restrict your players; and don't let them bicker out of character. If they have a problem with someone in game doing something, tell them to settle it in game. I had a player who talked all the time out of character asking in character stuff, and he always talked like: I say something to the wolf with talk to animals and ask him to tell me anything he knows about X. I told him to tell me what he said he'd say instead, because if he doesn't get a result he wanted, he would back out. Which leads me to another thing:
Fifth, don't let players act based on the roll. They roll a 2, they have to deal with it and suffer it, they can't say "oh, I'm going to stay behind because I bunked my roll", they have to go in, stealth and trip and make a loud fart or something to alert everyone.
Sixth, BE VERY CAREFUL WITH HOMEBREW. I almost caused a total party wipe in my 4e game because the final boss could gain maxHP and got stronger to the point he caused the new player to get insta killed. Same with items, and make sure if you do it, keep track of it. Rules you Homebrew should be maintained since you made or edited the rule.
Seventh, don't be afraid to push your characters in the right direction, but don't hold them by the hand. Give them a clue if they can't figure out what to do, or drop an NPC group talking about something.
Lastly: have fun. that's what it all comes down to
Hope this helps