Not sure about 'leaving tips' on hotel beds. I live here and seldom or never stay in hotels.

For waiters, yes you should tip 10% (or more if the service was good), but you either add it to the bill when you pay with a credit card (the bill will have a space on it to do this and the waiter will usually give you a pen). If you pay cash, you either tell the waiter how much change to give you back or you give him the tip after he has given you your change. If you leave anything on the table, the first person passing the table after you have left will pocket the money (and that may or may not be the intended recipient as very often tables are cleared by 'runners'). You don't need to pay the 'runner' or anyone else, as this will be sorted out by the waiter (most restaurants have internal rules on how tips are divided). Bearing the latter in mind, its probably better to tip a bit more than 10%.

The advice in the link by fozziedoggie on tipping petrol attendants and parking 'guards' is correct, although I use R5 as the standard. It needs to be seen if parking 'guards' actually safeguard your property or act like lookouts for the people you are trying to prevent from breaking into your car. So don't leave valuable in the car and if you have to, leave them out of sight (in the boot). I am suspicious by nature...