Congratulations on the new career.
My main advice is actually really simple. The important bits you will learn on the pitch, so concentrate on the following:
Look the part and act the part. Clean kit and looking professional is the start of effective match control. Before the game, be seen as someone with confidence and authority, arrive in plenty of time and do a proper warm up. Then, prior to ko, a nice confident blow of the whistle, get the Linos and the captains together and give them a confident, but short, talk about what you expect. It sets the tone.
Players are never, ever your friend. Be polite at all times and by all means engage in some friendly banter, but never let your guard down.
Always be consistent. If you let something go early, 9 times out of 10 it will come back and bite you later in the match. The same goes for what you say to players to explain a decision, keep it simple because, believe me, they will remember what you said and will turn it against you at the slightest opportunity.
I know this sounds a bit negative, but these are all things I experienced as a new L9 / L7. I look back on some of those games and shiver at what happened to me when I tried to be everyone's friend, lost a bit of concentration or just let too many things go.