While this can vary drastically from person to person, there's a few simple rules and concepts I try to remind myself of constantly.
For instance, I find that working to create a nice, provocative display with recognizable themes is as exciting as collecting the pieces themselves. I like things dynamic, cohesive and artsy. If a new statue or line of statues (well executed or not) compromises that, it's a good indication that I should pass. Last thing I want, or need, is a jumbled mess of pieces strewn about my apartment without any rhyme or reason.
Which brings me to my next point: Understand, and work with the space and budget that you have available. While everyone is entitled to their practices, buying everything you can get your hands on and filling a shelf/room/etc. to the brim with an endless amount of stuff comes off more like hoarding than it does collecting. That, to me, is a reckless, addictive approach to this hobby.. As appealing as everything may seem on a case by case basis, it all loses it's charm when breathing room is sacrificed for quantity. My collection isn't anything substantial, but I keep a list of all pieces and potential future releases that a). I know I can display appropriately should I acquire them, b). that I'm certain I can afford, and c). that stand well enough on their own or compliment what I already have,
as well as a list of my different display options/ideas. This keeps me in check for the most part.. with the notable exception being prints. I'm a sucker for prints haha.
Lastly, it's not the end of the world if you don't get around to picking something up. This is perhaps the most important thing to note. Collectibles are a luxury, not a necessity. If you kick yourself too hard for passing on a piece or missing a deal, things start to get considerably less fun which is an issue that speaks for itself. Relax, take a breather, don't let your decisions consume you, know your limits, set your standards and understand that nothing is truly a "must-buy."
Sometimes, it's as simple as kicking back and taking the time to appreciate what you already have. Life's too short to get hung up on a lighthearted hobby like this.