Do something to mark that first line perfectly straight - critically important! Whether you use tape or a marker THAT YOU HAVE TESTED, just make sure it is straight. Reminder, some markers become permanent when ironed, so what you thought you could damp wipe off, nope. Personally, I just like to use chalk that I brush off easily. A walking foot can make things so much easier, but it is not critical (if you don't have one). I also have a gauge that lines up with the previous seamline to make the keep the new seam an even distance (saves me from having to mark more lines). You can use a ruler or even a piece of cardboard cut to size. Point being, some of the tools make things easier, but you don't have to run out and spend more money.