Do you like music or like music tech? Post in some of the music-related threads.
How about sports? There are plenty of threads about sports, even football in the Community forums.
If you've read a lot about Macs in older threads already, maybe you could answer some questions that other people have?
Do you like films or TV shows? There are plenty of posts dedicated to movies and TV shows.
Maybe you are pondering your soon-to-be Mac setup... well, maybe get some ideas from some of the Mac setup threads in the Pictures forums, comment on other peoples' setups perhaps.
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The point of the 250 post requirement is that activity in the community breeds familiarity... familiarity breeds trust... trust breeds mutually beneficial transactions in the Marketplace. The reasons for this requirement are sound. Is it perfect? No. But it is much better than nothing.
Finally, getting to 250 posts is really not that hard. Refrain from "This." types of posts, contribute an opinion or thought... before you know it, you'll have 250 points. People may have gotten to know you, and who knows? Maybe you'll make a friend or two in the process.