So here's my experience based on my 57 levels of play-time:
1. Prioritize animals that give the following items in this order: Wallpaper, Preservatives, Cotton, Wood, Steel. Currently, I have every item that is craftable, and I am constantly selling off steel, wood, and cotton. In the beginning, I had a scatter-shot approach to having animals in my camp, and the result was me maxing out steel before everything else. If you play often enough, hosting the animals that give the rarer items is worth it. Go
here for a list of who gives what. As you can see by this list, the wallpaper and preservatives are only given by a very few amount of people, and while they are requested less, they are still the crafting items I struggled to get enough of.
2. Max tents first. It is the most important thing in the game if you want to continue to advance your animals. Make sure you're not focusing on any one specific tent-type and leaving the other types behind.
3. Kick out the higher camp-dwellers. If crafting materials are no longer a problem, make sure you only have low-level animals in you camp. If you play often, they will advance quicker, and you raise the collective rating of your animals faster by making sure no one is left straggling behind. It might seem tempting to go ahead and max out your level 18 animal by hosting it. However, this strategy in the long run will slow your overall progress. You can progress campers in your campground faster than if they were randomly located in one of the 4 spots. Thus, you really want to focus your campground attention on the lower level animals.
4. Tickets should never ever ever EVER be used for anything that isn't permanent. Extra slots? Use tickets. The KK Slider and Nook chairs? Arguably sure, use the tickets. But, speeding up a process or using them for the quarry is ridiculous. This is how these micro-transaction games make the bulk of their money--impatient people speeding up timed processes. I am very opinionated about this, so if anyone thinks otherwise, please respond so I can further elaborate why I stand behind this.
5. Have a comfortable, but not unlimited, respect for the "rare" bugs/fish. I have had plenty of theories about what a tuna or football fish is used for, but so far at level 57, none of the campers have yet to request one of the rarer items (not including the items that sell for 1k, which get requested often enough). I kept on hoarding these items until it became problematic (20 koi fish were taking up quite a bit of space), so I have a max of 10 slots dedicated to each rare fish/bug.
There are several generic theories about these rarer items. 1) They are worthless except for selling, 2) They are used in the late-game, and 3) Their uses have not been incorporated yet. Both the first and second theories would mean that you should not overload on these items, and as the third theory is simply speculative, you really should not hold these items out as the holy grail. Sell a portion of them or store them for later use, but dear god, DO NOT LIST THEM IN YOUR MARKET BOX.
6. Clean your friends list. You can have quite a few friends on your list that can help you with the quarry and with trading. That being said, if a friend hasn't logged on in two weeks, that friend likely has no trading use (all items slots are empty) and s/he will not be helping you anytime with the quarry. Prune your friendlist. My current cut-off is two weeks, and it'll get shorter as I accumulate more friends. (That being said, does anyone know how many friends you can currently have? I would like to know my limit so that I can better gauge when I should cut people off my list)
7. Make SURE you own the clothing or furniture that's listed in the market. I am a 100%-er, meaning I want to have everything I can possibly have. There are short-sleeve and long-sleeves versions of the same shirts and pants. You think you already own that fiery shirt? Check again to be sure you have the right type/cut of that shirt!
8. If you're suuuuper into the game like me, be the "go-to" guy for market items. I currently have twelve market slots that are constantly being bought up. The reason that my items are constantly being bought, as I would like to believe, is that I always have a set of three of every farmable item (the 3 fish from top-left, the 3 bugs from bottom-left, and the 3 fish from bottom-left). You need ANYTHING farmable?--come to me. I charge 150 per set of 3. This is not the cheapest of prices that I see, but because I always have one set of everything non-fruit/non-seashell, I feel like people often default to me to get what they need. For the last three slots, I fill those with my two "extra fruit," and then whatever other fruit I have in surplus. When I say extra fruit, I'm referring to the fruit-type in the top left area (everyone has a copy of all fruit types in top right, but the fruit types in top left are random for each player. I have apples and pears, and I always have apples and pears listed because those fruits might be more limited for other players and are often surplussed for me).