I have had five and am due Dc6 at easter.
Al so far have been easy, straightforward vaginal births, no forceps etc.
Dc1 was a long labour partly as I ended up flat on my back.
With the others I was more informed, made sure I stayed mobile in labour and tried to ensure baby was in good position before birth using birth ball, swimming, spinning babies info etc.
I was induced with all mine but still stayed active, even when I needed the drip with dd I insisted on staying mobile, using birth ball etc and dh backed me up against Dr's thst wanted me flat on my back on continuous monitoring. Had I just gone along with the Dr's I don't think my births would have been as straightforward, particularly as my babies were big ie 9lb + and Ds4 was 10lb 13oz with a 42cm head circumference off the top of the chart, he was born in birth pool. Had I done as Dr said and been on back on bed I don't think I would have had easy deliveries, I am only 5 2 and small.
So I think it's a combination of luck, genetics but also helping to get baby well positioned before and during labour.
My one baby tgat was back to back was more difficult to deliver but again being mobile helped and birth was three hours, had she been the right way round she would have shot out.
My back to back baby had anterior placenta which makes back to back position more likely apparently and not much you can do about position of placenta. This baby (30wks preg) also has anterior placenta so I just ordered a gym ball and have been spending my evenings on all fours etc to encourage baby into a good position.
Being supported and labouring in a midwife led unit rather than consultant unit helps your chances of easier delivery. Lots of things can affect how you feel and how you labour, so yes luck is involved but there are things tgat can help make a difference.