How do you insert the penis into the vagina?

In my case, in the missionary and woman on top positions, my partner usually uses her hands to guide it in.

Sometimes, i put the head of my penis between her buttocks and move it up until it starts to slip in.

Very seldom, things line up and I can just thrust it in. This happened once in a side by side position and took my partner by surprise and was immensely exciting.

I am interested in hearing other techniques.