I do all my tiling, take your time and start on the least used/ visible room/ wall. Top Tips- get a decent quality level and don't use large tiles on uneven walls.
You will probably find that the walls are not vertical, at 90 degrees to each other or to the floor. Nor will the floor be horizontal, thus the skirtings (if fitted) will not be horizontal. Finding the level for the first row of tiles is the key to a good job.
1 Mark out vertical centre line on each wall. You may need to adjust this to ensure window aesthetics are properly allowed for
2 Temporarily fix wooden batten one tile up from the bottom. take care with this stage, check all walls are OK to begin tiling at that chosen level.
3 Apply adhesive, I do two or three rows at a time. Leave the corners/ edges until last, work out from the middle vertical.
4 More adhesive, more rows of tiles.
All the advice above is useful, esp, the powered cutter. Buy 10- 15% more tiles than you think you need. Shops will usually take back unopened boxes although it is good to have spares 'just in case' in the future.