Start with a ch6 and work a tr in the 4th from the hook. Work a tr in the next two stitches. This makes your first ‘square’
Turn your work and ch6, tr in the 4th from the hook and the next two stitches, then ss to the space between the ch3 and the first tr on your first square. Ch3 and work 3tr in the same space.
Repeat the above for all the rows where you need to increase. You will work a ch3 and 3 tr into each square and you will ch6 at the end of each row as described above to increase.
Follow the chart attached. Each square on the chart represents a crochet square so you can tick them off as you go.
Once you have reached the halfway point and have done your final increase you are ready to decrease as below.
Instead of ch6, turn your work and then ss along the tr and into the space between the ch3 and first tr in that square. Ch3 then work 3tr in the same space. Continue along as you have been doing. You will turn and ss as described at the end of every row until the end.