It's hard to cover everything without being there in person. Generally:
You make the initial contact with your shoulder, and have your head off to the side. This will require you planting the proper foot depending on the shoulder and angle you're on.
You aim at their hips or slightly above (this isn't demonstrated in the following video properly until after 6:00). Either drive forward and up, or forward if you feel they're harder to take down. Aim to hit them and drive through, rather than just slide down their legs. Old school coaches advocated sliding down the legs, but it isn't the most effective way and you don't see it very often at a professional level anymore. Against a high knee runner, or a leading forearm you'll miss the tackle if you try to slide down.
Plant your foot close to the player, keep your head up and back tight, and grab them hard when you make contact. The best points to wrap the arms are around the waist and leg. You'd want to take both the waist and the leg in a rising tackle when you're trying to drop them hard, and mainly the waist if you're getting dislodged in tackles.
The further you are away the top of their hips, the easier it will be for them to bump you off.
Have a look at this. It's not perfect, but it's a good start and has a breakdown of the preparation for a tackle: