Do BAR CHORDS make you wanna head to the bar? Check out these great tips from seasoned ukulele players from the group "Ukulele Lovers":

1. Use a strap to take the weight of the ukulele, and remember that gravity is your friend. Letting the left arm feel heavy, downwards, is much more powerful, and easy, than using your hand muscles to squeeze. 
2. While this is a guitar site, I have learned a lot from this person's videos, including good barre chord habits. https://classicalguitarshed.com/make-bar-chords/
3. Practice one barre chord, same one, 5 minutes a day till you get it; really take your time. Pluck the strings individually, notice where the strings sound good and where they don't, and how that relates to what you're doing with your fretting fingers. Be slow and mindful and correct the problems you find. Rinse and repeat. 
4. Use your strumming arm to grip your uke tight (but don't tense!) - you can 'push' your uke into your fretting hand fingers - if you get it right, you barely need to grip the uke at all with your fretting hand. At all costs avoid the fretting hand 'grip of death' it causes so many problems! Aches, pains and problems changing chords fast…
5. Start with only your index finger over a whole fret and support it with your middle finger. Then add your pinky to your G string, skipping a fret to make the regular minor. You'll feel comfortable at some point to use your middle and ring fingers.
6. Google Christopher Davis-Shannon, Phil Doleman and Stu Fuchs (Ukulele Zen) to see their YouTube videos on barre chords or specifically the Bb chord. They have lots of really good advice to avoid damaging your hand. It is all about technique not strength. Be careful, I initially hurt my wrist by doing it wrong and compensating by pressing harder. Practice in front of a mirror to check your action matches what they teach.
7. The side of your forefinger will cause less buzzing than the palm side of the finger. So think “elbow in”. Move the Uke slight to the left, so your elbow is closer to your waist and get the inside of your wrist closer to the neck. Don’t exaggerate, just position your hand closer to the neck. 
8. When you use barre chords, you will use all of your fingers. Beginners concentrate on using index, middle, and ring, while ignoring the pinky. A good tip is to practice forming chords using all fingers. Experiment with different fingering for different chords. Examples: play C by holding 1st string 3rd fret with pinky instead of ring.
9. Get the action (string height from fretboard) as low as you can. The less pressure we need to apply to the strings, the easier it will be.

Have you mastered bar (barre) chords? What's your best tip?