Mostly just common sense things can make a big difference.
- Be on time consistently. You're the professor and should be there to open and close, except for the odd day where you're sick/on vacation and need someone to cover.
-Have a reliable backup person or co-professor. (In case you're sick/on vacation) You might not have this at first, but once you have some regulars start coming try to notice who you think would be reliable enough and you would trust running the league for a day if needed.
-If you can, have a couple extra decks to play against each other or your own "Weak" deck, at least when starting out in a brand new environment. This is really helpful for new players who don't have their own deck, or just have a theme deck. Your own tier 1/2/3 deck will stomp them so having your own unmodified theme deck or just a silly one will allow them to feel like they had a chance. Doesn't mean you have to let them win, but there's a big difference between something like a Volcanion deck that hits two max elixirs on turn 1, and a silly Frosslass deck that can still win with decent coin flips. It's hard to feel good going against a kid's mash up of EX cards in their random deck they built with the first example, while the second example will show them some cool abilities while still allowing their deck to function. Don't use expensive cards if you're supplying a "Guest deck." I've seen some kids shuffle and it hurts to watch sometimes. XD
-To promote it, get it listed on the Pokémon Website, the store's website, a flyer in the store if they have a board or just post it at the cash register if allowed, use the social media you are comfortable with (Facebook and Twitter are probably the most popular) If you have any contacts or know any kids at a school/church/club thing see if they would be interested and have them bring a friend. (Prize packs/extra promos for whoever brings the most friends during your "Launch month" as a special event?)
-Also, while it may seem counterintuitive, check out the other local card shops and leagues in the area. If their Pokémon night is on a different night than yours ask if their Professor would be willing to promote yours or if you can attend and promote it yourself. (Obviously attending isn't an issue, but double check if you can promote yours if they are competing stores) If it's on the same night I wouldn't feel comfortable doing that though as it could be seen as trying to steal players. I'm fortunate to live somewhere with Pokémon happening four days a week within a ten mile radius across three stores and a college. Many players attend a few of the leagues a week. (I attend two regularly myself) The Pokémon community is pretty friendly even among "Competing" stores.
-Keeping friendly communications open between the other local leagues will also help allow you to schedule Pre-releases and other tournaments around each other outside of the regular league night once you get to that point. As long as they are all on different days I attend as many events as I can, but if they conflict I definitely have a preference between who gets priority. (Happened a couple of times) The third store in my area just recently just started their Pokémon scene in the last two months, and since it doesn't conflict at all with my main league literally half of the new league is made up of people from my main league because I advocated for it so our area can get an extra place doing Pre-releases. It's great for both stores as they both benefit from the increased traffic and friendly word of mouth between them.
-Have a consistent way you give out promo cards. My main league gives out one per person every week provided you sign in on the paper sheet. Here they have a good supply of various older promos to choose from since they have been running it for several years. My secondary league gives out one per person each week, up to two promos a "Season." (I think seasons are about a month long) Since this league is really new they want to have enough to give to all players without running out. Sign in for this league is done via the stores free loyalty card that stores our Pokémon ID also. Shouldn't matter if it's one per week, or a limit per season as long as it's consistent. (But can change once you build up enough stock, just don't go back and forth each week)
-Most importantly have fun! If you have other leagues in the area find out what they did when they started.
Hope this helps!
