Having attended and twisted at hundreds of birthday parties across the UK, I have been fortunate to see countless real life examples of what works well, and what works not so well.

Venue
Choosing the right venue is an important first step. Pick somewhere local, and make sure they allow whatever entertainment  you are hoping to provide. Also check for suitable kitchen and toilet facilities.  And also parking! Local Village Halls are a great starting point, and often very affordable, from £5 to £15 per hour.

Dates and Guests
If it's a party for a child attending school, check the birthdays of other children, and make sure their parents aren't planning for the same date - Nothing worse than a clash!
If the whole class is coming along, invitations taken to school is a good way to make everyone aware. If it's a smaller gathering, try to get the word out in other ways, to make sure nobody feels left out.

Food
Simple is key here. Remember your audience!  Depending on your budget, finger food such as sausage rolls and sandwiches always goes down well. If the venue has a kitchen, why not make use and cook up some pizzas, chips, chicken etc. Check with parents for any allergies or dietary requirements. Set some time aside for the kids to eat, and remember to provide lots of easy to access drinks.  (Plus hot drinks or maybe a tipple for the parents!)
I've recently seen a trend of individual buffet food portioned in pizza boxes for each child. This worked really well, was great for anyone with allergies and also helped keep mess to a minimum!

Entertainment
In my experience, amazing party entertainment can be as simple as musical statues, all the way up to bouncy castles and nerf guns! When hiring entertainment, make sure they have suitable insurance  and are operating safely.  If hiring a bouncy castle, ensure the drop off and collection suits the time you have your venue.  Balloon twisters (such as Mr Twists) are always a hit, as are face painters and magicians. Bring your own speaker, or borrow a friends and get a good kids playlist on Spotify  (without adverts!)

Relax and have fun!
The children will make their own fun, and before you know it, it will all be over! Ask another family member or friend to take photos (check with parents before publishing anywhere)  to help document the special occasion. Enjoy tidying up and start planning again for next year!

Mr Twists is more than happy to provide no obligation advice on planning your party, we want every single party to be extra special.