After I got ^really^ stressed out by the school playground when dd started, I've now completely relaxed and when ds started I was really chilled.
I was lucky enough to find some really close friends at my original ante-natal class, and nearly 9 years on we're still close even though all our dcs go to different schools. I thought when dd started school I would find similar. I didn't. I felt fairly out of place.
However, I stayed friendly and chatty and a few years on I have actually found some good friends at the school who I see socially. They are not my closest friends but they are fun, friendly and generous. Half of them are not from my dd year let alone her class!
My dd has 'chosen' some friends who I don't know their parents at all. One boy she particularly likes is the youngest of 4. One day at a party I found his mum and made myself talk to her. She was really nice. She said she couldn't be bothered at all with the 'school gate' as she'd been through it 3 times before. She just slips in and out with minimal fuss. I liked her attitude.
The school gate is what you make it. Some days I'm standing in a group talking to my friends. Maybe people see it as a clique? It really isn't. It's just a group of friends. We would never turn our backs on anyone.
Other days I stand on my own or talk to someone new if the chance takes me. It really doesn't bother me now.
As others have said. Smile. Be friendly. Just do your own thing with confidence. Believe me, people are too busy to care too much or ^notice^ how you may perceive things.