Starting simple with training is easy. The main goals in training a plant are to control growth, and maximize canopy. Cannabis plants are very resilient and can take a good bit of abuse if you give them good conditions to live in and recover afterward.
If you have 3 seedlings starting you could do different training on each to see what happens. I like to use a combination of techniques to shape plants when I train them. I will usually use LST, and tie branches down to the edge of my pots to keep them where I want them to grow. This allows us to build a strong set of lower branches which will help support our buds on top when they start. LST is also a good way to spread the plant out horizontally to control the level of the canopy which allows you to keep the light closer and have more buds sites getting the light. As you spread the plant out more side branches will get light and reach up to become good bud sites.
I also use topping to create more bud sites and control size/growth. When you top a plant, or a branch it will typically grow 2 new branches or tops from the previous node. So you can take a seedling and top it and it will have 2 tops after that point. When you top it, the other side branches will also usually push out more since you stopped the vertical growth. Once it recovers and the tops grow up a couple more nodes, you can top those, and then you have 4 main tops, and your side branches might be almost equal to your main tops. Do this one more time and you have 8 main tops, and 4-8 side branch tops as well that you can top and split if you want, or just let them grow depending on your space and light penetration. All through this is when I would use the LST to control the direction and height of the side branch growth, and even the main tops if necessary. My whole goal is to have an EVEN canopy with many bud sites.
Hope that helps some.
