Start by finding a suitable spot. The spot should not have another side accessible from another side at a distance less than your character side.
Crates are a good way to practice. Keep in mind that many crates are patched so that you are killed if you try to enter them BUT many of them you can survive in if you keep to the edges. A good technique is to face the object at a 90 degree angle very close to a corner. Knife the wall once or twice. You will notice that your character seems to move slightly into or towards the object. If you seem to be closer, shift run into the object. If nothing changes either slide along the object or jump if possible. Some spots you can simply fall into because of nexon's pure fail attempt at map building.
Thing's such as box corners and round objects are sometimes pass through. An example of such spots are the arches in the bottom of Two Towers.
Give it a try.
Using those techniques or and or others on the site PLUS the melee mods will lead to Glitching successfully!
If anyone would like to have an In Game glitching tutorial feel free to pm me and we can arrange a time.