General advice

General advice for lectures (particularly for new lecturers)

Ensure that the lighting for the students is adequate at the start of the lecture. In some theatres the lights are permanently dimmed for projector use. Therefore it is useful to know beforehand how to alter them. Any problems with lighting, seating, ventilation and temperature should be reported to the appropriate building manager as soon as possible after the lecture.
In week one of each semester students must be informed of the fire exits from the lecture theatre.
Ensure at the start of the lecture that nothing blocks access to the fire exits. In some departments equipment has been left in front of the exits and it is the lecturer's responsibility to ensure that it is moved before the lecture; even if it seems to be regularly replaced by subsequent lecturers.

It is usually a good idea to check out the proposed lecture theatres (especially if in another department) to ensure they have adequate provision. For example: the white/blackboards are sufficiently large; there are decent powerpoint and document projectors; supplementary equipment (laser pens etc) are easily accessible. If there are problems then discuss this with the pre-lecture contact person.
The lecturer should ensure that they have familiarised themselves with how any of the equipment (microphones, laser pens, pointers, computers, various projectors) they will use is operated. A technician may not be immediately available when a problem arises.
Check whether there are whiteboard dusters in the lecture theatre. These appear not to be provided in some theatres.

Be sure to check through any calculations that you intend to use in the lecture. This ensures that you do not make any elementary mistakes in the lecture itself and cause both confusion for the student and embarassment for the lecturer. This is particularly worthwhile the first time a module is delivered.
It is useful practice, if practical, to arrive at the theatre five minutes early to check the facilities and organise how you will use the equipment. Arriving at five past the hour and then beginning at seven minutes past is unfair on students who may have been in the room for ten minutes already.

Lectures must start on the hour and finish at ten minutes to the hour. This allows five minutes for the previous class to leave and five minutes for the next class to enter. Continuing beyond this point is not only unfair to students, who may have need to get a lecture in another building, but discourteous to the lecturer who is waiting to get in.
Ensure the doors to the theatre are closed at the start of the lecture to reduce external noise for the students closer to them: this also signals to the students that the lecture is beginning.
If the lecture theatre seats many more students than the number who attend (either in general, or on a particular day), it can be helpful to instruct students to sit in a block in the centre and towards the front. This makes it easier to direct the lecture to the class as a body, and to control the class. Directing latecomers to the front part of the lecture theatre as they come in can also help to encourage punctuality.
The clocks in theatres may not be correct - either too slow or too fast or stopped. Alternatively the clock may not be visible to the lecturer. It may be a good idea to leave your (accurate) watch beside your notes, so that you can check the time periodically without continually looking at your wrist. This is particularly useful after around halfway as one can gauge how much more material can be covered at a reasonable unhurried pace.

Be aware that in many lecture theatres parts of the board are blocked by some or all of: computer screen, lectern, table, overhanging pelmet. It is a good idea to check how much of the board can be seen from various positions in the room, and to draw lines on the board sectioning off any invisible sections before the lecture begins.
Unless there are very good reasons to do otherwise, it is a good idea to start at the top left of the left hand board panel and work from left to right. Students, particularly those who write slowly, also find it confusing if some material is erased on part of a board panel and new material is added at that point.
Students at the back will not always complain if your writing is too small. It's worth going to the back of the room at the end of occasional lectures, before cleaning the board, to check that what you've written is visible.

The white/blackboards ought to be cleaned at the end of every lecture. For whiteboards this will help preserve their quality.
If the whiteboards are particularly dirty, they can be improved with the occasional wipe with a cloth damped with water. This is invariably better (and more environmentally friendly) than a solvent.
If using water to clean blackboards, please don't use the felt erasers as the felt hardens and they stop being effective when they are wetted.
The blackboards can be kept reasonably dust free by ensuring that the duster itself is kept dust free. This is achieved by scraping the dust off by using, for example, the edge of the board ledge. Otherwise one is simply redistributing the dust on the board and not removing it.