It helps if you can fix as long a baton as possible to the wall(as a guide) and place the first row of tiles onto it. It isn't always advisable to tile directly from the skirting upwards unless you aren't fussy about how high you want to go. Also the skirting may not necessarily be a perfect line.
Don't do one little spoldge of adhesive but do as much of the line as possible.
Wherever possible work back from the corner that is going to show thus leaving(unless you are very lucky)the cut tiles in the corner that you won't notice too much.
Have a look at this site.
http://www.helpwithdiy.com/tiling/set-out-wall -tiles.html