(Blogger STILL isn't posting pics, so I've hosted these in photobucket. I'll replace them with clickable ones when Blogger is working again!)
By popular demand, this is how I park my threads...
I only use parking on my HAEDs, and the main reason I do it is because my tension is quite slack. I find if I stitch normally (doing all one colour in a section, then moving on to the next), my stitches look lumpy over 28ct. They're fine over 25ct, so I'm not parking on Tomboy. And I don't park on the Carriage House Samplings alphabet because that just uses a few colours. But HAEDs are solid stitching with lots of colour changes, and it's hard to get stitches even if your tension isn't tight. That's all just to explain that it's certainly not necessary to park your threads on a HAED, or even to stitch in blocks or rows. It just works for me.
I stitch in blocks of either 10 x 10 or 20 wide by 10 deep. I stitch / then \. I work in rows, moving left to right along the first row, then right to left along the second row, etc. I stitch and finish one stitch at a time.
I start with the first colour in the top left corner and stitch each stitch in that row of that colour, moving from left to right. I then find the next stitch down of that colour, either on the next row or further down the block, and pull the thread through to the front so it's at the bottom left corner of the stitch, ready to do the first leg /. I then pick up the next colour in the first row and do the same with that one. I keep working along the row until all the colors are done, and then I work back along the second row, picking up the threads that are already there ready to do the stitches, or starting new ones if it's a new colour.
As long as I count correctly, the threads should always be in the right places, so I just pick up whatever thread is there and assume it's the correct colour. After a bit you get to recognise what threads match what symbols, so you know if something's in the wrong place. If there's no thread there I need to start a new colour. I have one thread for each colour used in that block. (If you look at the pic you'll see lots of threads under the detailed bits but only a few under plainer background.)
I basically zig zag down each block. Sometimes a block is only a couple of colours and it's fast. Sometimes it's 20 or 30 colours and it takes ages. I rethread the needle for each colour - it doesn't bother me - although if there are only a couple of colours I have two needles, one threaded with each colour, and just pick them up as necessary.
This is the basic way I park threads. I know other people do it differently. To speed things up I do stitch beyond the current row occasionally. My main rule is never stitch a stitch unless there's one above it. So, I will stitch right down the block if a colour is used under ones that are already there. If you look at the close-up of Air you'll see that I've stitched all the blue, and the darkest colours, because they fall under each other. But I haven't finished the ends of the last few rows yet because they need new colours.
I hope this makes sense! It's quite hard to explain. Any questions, please ask and I'll try to explain further!