Sorry you didn't enjoy it.
I have done it and find I just had to be really organised. Travel sorted, accommodation suitable and activities planned - or at least a good idea of what we might do (good weather or bad).
Things like the beach - I needed somewhere semi secure to put our stuff - so I got a beach tent with a zip up front, so hopefully I would have a few minutes warning if someone tried to get in and get things while we were playing or nipping to the loos.
Know how and when to feed the kids. If we were overnight I would usually have picnic stuff for day 1. Premier inn breakfast for day 2 etc.
There have been disasters- when someone was sitting in our train seats on a long journey on a busy train and wouldn't move - I had 3 little ones with me - one in a sling, with all the luggage and a pushchair. (A friend tweeted the conductor for that one as i couldn'twalk up and down and find him)
When we got back to a hotel and kids were too tired to go out for tea and the pizza ordered never arrived....so I cancelled it.....then it did arrive an hour later......after we had raided the vending machines for crisps and chocolate....
There have been plenty of nights at relatives where someone is ill, or can't sleep, or they tag team not sleeping.....
An open mind, a sense of humour and not too high expectations help. As the kids get older it gets easier.
And our disasters are now tales that we tell.