First make sure that in Aperture all your photos are "referenced", not "managed", that is in normal Finder folders rather than hidden inside the Aperture library. This means using Aperture's File > Relocate Masters menu command to move the managed files from the Aperture library and into regular folders. If you want to keep your project structure, Relocate Masters has suitable options.
While Lightroom can't read Aperture adjustments, it's important to remember that it can read keywords and other IPTC data that you entered in Aperture. Use the Aperture 3 command Metadata > Write IPTC Metadata command (there's a slightly different method for Aperture 2).
You can then register or "import" the pictures into Lightroom, making sure you select "Add" in LR's Import dialog. This leaves the files where Aperture knows they are, and as a strategy I'd suggest leaving the new "ex-Aperture" folder structure (the one created by Relocate Masters) exactly as it is, and never renaming or moving any of the files or folders that are in there. Leaving things this way it's easy to go back to Aperture whenever you want to reprint one of these legacy pictures with their Aperture adjustments.
With new pictures, just put them into a new folder structure. I'd recommend simple date-based folders. So all your work would be under a couple of top-level folders - "ex-Aperture" and "Photos". You don't have to do this, but it's easier if for any reason you do want to refer back to Aperture.
