I've organised a few trips and go across at least twice a year. To get a good overview of both the salient and the Somme will take three full days. My advice would be for a first timer to engage a guide after determining what you want to see. The professional ones are excellent and fairly reasonable. On the salient I would split it up and on the first day take in the southern part. Messines Ridge, Hyde Park Corner, Ploegsteert Wood. Going north up to Sanctuary Wood, Hill 60, Menin Road, Ypres itself and Yorkshire Trench.
The Somme is a fair old hack down the road but Arras and Vimy Ridge are on the way. Newfoundland Park is a must and drive along the old front line south to Beaucourt-sur-Ancre and on to Thiepval Monument, Delville and Trones Wood, Sausage and Mash Valleys. Bite to eat in Albert. Lots and lots to see.
Back to the salient the next day and start in Poperinge and TOC-H working around the northern side via the casualty clearing cemeteries to Poelcapelle and Passchendaele and Tyne Cot.
Hire a good guide and you will see far more than the bog standard bus trip gets to see. You choose where and he will take you. Enjoy, it is a marvellous place to visit. If you want any specific info please PM me.