If your sauce is too thick and the flavour is too strong you simply need to add a little water.
If your sauce is thick but the flavour is perfect do not add just water or your flavour will be diminished. If you have used a stock cube make a little extra of that stock in a jug with boiling water (1 cube per 500ml water) and add a little at a time to your over-thick sauce.
Do not add extra alcohol in a recipe at the end of cooking. Wine and especially beer change in flavour as they are cooked and can be harsh at the beginning of cooking. If you add a dash of beer to your Steak, Guinness and Stilton pie mixture, for example, at the end of cooking it will taste very bitter indeed. Add a little more beef stock instead.