I usually do not prick out seedlings too early, so by the time I do it, they have grown into each other. The up side is that the plants are larger and easier to handle. the down side is that I usually damage some of the roots as I transplant them.
I first decide how many plants I want to keep. I rarely want more than 6. I then split the seeding pot into 6 sections and pot them up. This might give me a dozen seedlings in each new pot. I let this go for a week or so to see how the transplanting went. I then take scissors and cut off most of the excess seedlings. I leave a few in each pot. As they grow, I thin them again, until I am left with one in each pot.
This way, I rarely end up with empty pots.
The above is used for seeds that need cold treatment, since I grow these outside in winter (unheated sun room) and let them sprout naturally in spring.
For seeds that can sprout warm, I prefer a completely different treatment. I sprout the seeds between two layers of tissue paper, that is kept wet. As the seeds just start to send out their root, I pick up the seed and plant it, usually 2 or 3 per pot, depending on the number of seeds. I end up keeping just one seedling per pot.
I really like this seeding method since I can tell exactly what is sprouting and I don't have a lot of pots sitting around that never produce seedlings. There is also no transplanting of seedlings.
For sprouting I use small parts compartments - these have small plastic trays, maybe 12 or 24 to the box. Found at hardware stores. Each drawer has one type of seed in it.