I’d say start heelside, I know some people think toe is easier but I think you can gain a faster understanding of sliding heelside and it’s all about moving your body the right way at the right time
More than anything it comes down to practice, practice, practice the whole wax on wax off business. You’re going to fall it’s part of it wear your helmet and your slide gloves it takes a fair amount of force to break wheels free and I would recommend learning how to slide with gloves first to get a feel for it and to break your wheels in standup sliding does not come easy at first. really push your leg out and try not to lean too far to any side.