churning is dead, most all of the cards have some kind of waiting period between bonuses, you have to search the individual card program to figure the suggested waiting time between applications, cancellations, and new applications in order to qualify for signup bonuses more than once.
App-o-ramas are foolish for the most part...only show off bloggers like FM will suggest signing up for a dozen cards, the only possible reason to get 2 cards at once was to save a hard pull on your credit report by the card company (two pulls in the same day would consolodate into one) and credit card companies look at how many pulls you have on your credit report. The people that do app-o-ramas usually consider which of the 3 credit agencies a particular bank card will use for a pull and apply for a spread of cards that don't use a single agency too many times. The problem is they are usually greedy hogs feeding at the milage trough and will eventually paint themselves into a corner. You can apply for 10 cards at once but that sends up red flags to banks that think people are trying to get a bunch of credit at once (which they could then default on) The card companies see how many cards you have in the next attempted app-o-rama and eventually you will be denied for too many inquires, too many cards, too much credit, average account life too short, or a multitude of other reasons...
I've found the best way is to go slow and steady, keep some no annual fee cards open forever, and apply for a couple of cards from different banks every 4 to 6 months, keeping them for a year or more if the benefits are worth the annual fee, and cancelling them as needed to make room for new cards from the same bank, if you are denied a card it is easier to be reconsidered and approved if you cancel another card from the same bank and use the credit you free up to be approved for the new card. There are many subtle methods to learn for each program, and if you go slow, you are more likely to stay under the radar and make less mistakes than a person doing app-o-ramas every 3 months. Your credit rating is more important than a bunch of points, don't screw it up just because a blogger told you you could get a million points easy.
I would say the most important thing besides protecting your credit is to know that you can be financially responsible, if you can't pay off your balances in full every month and use cards as tools to get miles, you can get into trouble quickly.
Like someone else said it is good to have a plan, so you don't wind up with a bunch of unrelated miles in different programs. Figure out which airline is best for your home city and start with them, read their progam info, look at their website and learn how to earn miles, be aware they have many partners that you can earn miles with. Know that the best point bonus offers are the least advertised ones ( FT is a great source for finding the best offers out there) sometimes the airline or card company will send targeted offers for high bonuses through US mail or e-mails, so get on their mailing lists. Figure out if any other credit card points transfer into your preferred airline program (example 50k United points are great for signing up for the chase credit card, and will get you a domestic round trip coach flight for 2, but if you get an American Express card with membership reward points and transfer them into United, you suddenly have enough for first class domestic or a pair of coach to Hawaii)
If you are able get business credit cards for additional bonuses, they are treated seperate from personal cards and don't effect your credit score in the same manner.
Business cards should be added slowly as well to build credibility, unless you have a active business that you can put a lot of expenses on the cards.
Once you get enough airmiles in a program, you may want to add a hotel program.
Once you have air and hotel, a chase card that earns ultimate reward points, a Amex that earns Membership Reward points, or a capital one venture card that earns travel points are good to have for other travel expenses like rental cars or other travel related costs that are not covered by air or hotel points, these are also good to have because you can transfer the points into your air or hotel program if you need a few more points to get an award.
So now you know, to focus on learning how credit works, focus on a few reward programs that will work for your origin or destination cities, research all you can directly from the reward sites, and from the associated threads here in FT....search and read, most things have been asked and answered a hundred times here. Take your time, a few months of reading and asking questions will help you get a handle on it.
See the big picture first, then focus on the details, remember slow and steady wins the race and will earn you more points than you will have use for. There is no need to treat this like a slickdeal and sign up for a dozen cards just because some blogger did it. Most of the ones that are doing app-o-ramas have been playing this game for a long time and have worked their way up slowly until their credit can handle the load...if they just started and are doing app-o-ramas they will learn the hard way.