To lay pavers in a straight line, start by running a string line along your edge, one paver in distance from the wall. Hammer in a nail at that point and tie string around it. Then measure the distance from the wall to that string line point. Mark this distance out on the opposite side of your paver area. Hammer in a nail and run the string line from the other nail to it and tighten the string.
Use the spirit level across the length of the paver to make sure it's level. Give it a tap with the mallet to even if out if you need to. Use a spirit level to check it diagonally as well. After making it level, just make sure the paver is still flush with the string line.
A good tip after laying a paver is to wipe the top of it with a damp sponge to clean off any mortar. It's much easier to clean now than later when all the pavers are laid.
For the second paver, spread out the 30mm of mortar needed to lay the paver on. You can use a trowel to help you do this evenly. Lay the next paver on the mortar 5mm gap from the first paver. Then use the spirit level and the mallet to make the paver level like before.
Continue laying a bed of mortar down and placing pavers on top in line with the stringline. Make sure you keep a 5mm gap between each paver, and that you use the spirit level and mallet to make sure every paver is level.
If you'd like to lay pavers in a stretcher bond pattern, mark out the middle of the paver you'll lay. Then lay the paver so that its middle is aligned with the 5mm gap between the first and second pavers in the row. Keep a 5mm gap between the first and second rows.
As you lay your pavers out, it's a good idea to always make sure that the row is straight. You can do this by running a straight edge along the pavers. This will ensure that you're laying them down in a straight line. If necessary, adjust the pavers with the rubber mallet to straighten them.
Often you'll need to fit pavers at the start and end of each row. To do this, measure the distance between the end paver and the end of the paving area. Deduct 5mm from this distance to take into account the gap between the pavers. Then mark out the measurements onto a paver.
Continue measuring, cutting, laying and cleaning the pavers until you've paved your whole area. Just make sure that every paver is level and each row is straight, and that you've kept a 5mm gap between all of the pavers. Then give the pavers at least 24 hours to set before you walk on them.