First choose the right tools. Here is my standard tool kit: short shuttle (14" x 1 1/2"), long Shuttle, scissors, flat tip screw driver, tacks (#6, 1/2"), tack hammer, 12" &, 6" rules. Also you must have a spring clamp like the green one you see in the second photo.
Here is how I clamp my chair into place on my bench just for chair making and weaving. I have a slot in the middle to run clamps through. I have a set of leather golf gloves with the finger tips cut out and fingers wrapped with athletic tape. These are not necessary if you only plan to do a couple chairs.
Something that is key to laying out the pattern for a variety if weaves is knowing how much cord will fill a given area. A general rule is 7 cord widths for every inch for standard Danish paper cord.
For example, If I have a space left near the end of weave then I want to avoid having too much cord or worse not enough to finish, thus another knot exposed on the bottom. So to figure the exact amount then just measure the gap. One inch equal seven wraps left. As in the weave shown above, remember that one wrap is all the way from front to back. So if your chair is 16" from front to back then one wrap is 32".
If you practice doing this you can eliminate many of the knots from showing in the final product. The photo below is the bottom of one of my chairs. They don't all turn out this well but it is great when the bottom looks as good as the top.
A clean way to tie off the seat is what I am showing below. To keep it tight while making the knot just wet the area that the knot will land in. Slip it under the last weave that came through the seat (so as to not disturb the tension in another area of the weave by mistake) and bring it back through making a standard knot as shown.
Take the end and simply slip it in between the cord layers. That's it, your done.
If you have any questions let me know. I will try and answer what I know.