as others have said, controlling your speed is key.
Start with foot braking, carving and then learn to slide.
Checkout Lush Longboards as well as Arbor, Sector 9 and Never Summer
A vert skater once told me that Longboards are for folks who can’t skate anymore and there’s probably an element of truth in it. If I ride a shorter board they feel really nervous and twitchy. But longboards are great for getting your ‘carve on’!
Key for me was finding somewhere safe-ish to ride and practice – ideally you want nice traffic-free smooth, flat (i.e. no camber) stretch of tarmac gently sloping downhill with a good ‘run out’
Since the best places are often public roads a helmet, gloves and pads are recommended. Tarmac really does hurt/rip your skin off.