In World War I how did English soldiers travel to France? Were they in good conditions?I have to write a letter home from World War I to family...

There is a website call the "The Long, Long Trail" that might provide good background research for your question. You'll find it here: http://www.1914-1918.net

There are also letters from soldiers online: http://wwar1.blogspot.com/

In general, the British soldiers were transported several ways. They tended to take the train in Britain, to get to recruiting or training centers. Once trained, they were back on trains or trucks and then to the ports. They then took ships across the water to France. Once in France, they were back on trains (if they existed), on trucks, or, for a lot of the final distance, marching on foot. Conditions varied. The original trains were fine: they were civilian trains. The later ships were very crowded—but the distance was small, so conditions weren't too bad. However, once in France, conditions got bad indeed, as they were often marching into battle, under fire, or into poison gas.