Preparing your vehicle for your rolling road session is very important to get the best value from it's time spent here whilst it is being worked on and for the safety of both your vehicle and the equipment operator.

Please take the time to read and undertake the following advice before presenting your vehicle for testing or tuning.

Tyres:   Ensure the tyres are in good overall condition showing no defects that would cause them to fail an independent inspection. That they are less than 8 years old (search how to read DOT tyre code), are all inflated to the correct pressure and suitable for the load/top speed potential of your vehicle. That they don't come in to contact with any static components or bodywork, that wheels are not buckled or out of round.

If you are bringing an off road vehicle that they are suitable for road use.

Fuel:   Ensure the vehicle has a sensible amount of good quality fresh fuel in the tank. When tuning a vehicle it will often require being run at high speeds, under load or both and may cover around 50 or so miles in a session, with this in mind we have the potential to get through a fair bit of the flammable stuff. Obvious perhaps but you wouldn't believe how many vehicles appear with gauges hovering near the empty mark with owners anticipating us to do our thing!
It is also important to bring the vehicle with the rating/brand fuel you would normally use in it. There is little point to tuning an engine to run best on fuel with racing strips if your normal fill is less potent, you also increase the risk of potential engine damage long after your visit by not taking this advice.
Ensure that there are no system leaks and the system has adequate protection from heat sources where there is a potential risk, especially from melting through hoses or plastic fuel tanks.

If you are bringing a track vehicle with a small tank, please ensure you provide enough extra fuel in a suitable container with the means to add it.

Fluids:   Ensure all fluids are at the correct level (engine oil, coolant, gear lubricants). That there are no leaks or the likelihood of overflowing with no catchment. That any connecting hoses are suitable for their application, secured properly and not likely to come into mechanical contact, be worn through, overly stressed or get forced off. The coolant is entirely bled and cooling fans are working.

If radiator cooling fans are operated manually, be sure to tell the operator that the fans are NOT automatic and there is a means to monitor engine temperature provided.

Transmission:   Ensure it is in good overall condition, engine/gearbox mountings are up to the job, rotating components balanced and safe for their potential RPM, operating speed and torque output of the vehicle. This includes shafts and automatic transmission torque converters. That flywheels if lightened have been done so to a reputable standard. That the clutch both clears properly and to your knowledge doesn't slip under full torque being applied. Any bearings, flexible joints and their flexible coverings/boots function as intended and are properly secured.  Wheel bearings, suspension and related components are in sound order.
Very importantly, that wheel nuts/bolts are tight and preferably torqued to the recommended amount.

If any sensors are faulty or known not to be working, repair or replace them, especially fuel injection system related. If a gauge doesn't work or is suspect make the operator aware.
The exhaust system is leak free, properly mounted. Not overly loud and exits in a sensible place to position exhaust extraction and monitoring equipment.
For tuning it's preferable that you have an oxygen sensor boss fitted to the exhaust near the engine in a readily accessible place so we can fit our monitoring equipment in stream for more accurate results. The boss ideally needs to be positioned in the upper third portion of the pipe to avoid condensation damage to the measuring sensor, with ideally around 15 to 20 cm free space above for the sensor body and its wiring.

The chassis or any components aren't abnormally low preventing the vehicle accessing the rollers or having bodywork which prevents making securing the vehicle for test difficult or impossible. If you have any information about the engine build it helps to make a note of it and bring that with you. If the engine hasn't been run in or has a known RPM limit make the operator aware. If possible all engine timing marks are accurate and clearly marked. Your valve timing drive is in good order and tensioned correctly. Check your throttle system is able to reliably return to closed/idle position and achieve the fully open/maximum position.
If you have any relevant spare parts bring those too, as if they are required will lower any potential parts cost. If you have any component operating instructions, connecting leads, software etc, bring them along as it all may speed up the process.

Any finally, please ensure your vehicle is presented relatively clean, oil and coolant leak free. For example, off road vehicles arriving covered in the previous outings mud and cr4p will be turned away. Engine and transmission fluid leaks naturally happen that owners are not aware of whilst the vehicle is used, particularly with heat and stress whilst putting vehicles through their paces that only become apparent in the same circumstances whilst the vehicle is not in motion, this is to be expected. However vehicles that leave an abnormally sized slippery mess behind may be charged a clean up fee on top of the work performed. 

The above guide is not meant to intimidate, following it's advice you'll hopefully arrive with a suitably prepared vehicle less likely to suffer issues, hopefully also not costing you wasted time or having you sent away being unsuitable or not ready for work/testing.
Most vehicles well maintained and in regular use that can successfully be driven full throttle down the road will not have a problem on our dyno. Problems usually only occur on recommissions or new builds that have not yet been tested as often the dyno is its first test, when naturally any issues will show up.