Some conventional methods are finding a good catalyst, condensing a product from gas reaction, removing a gas byproduct from liquid reaction, change of temperature and pressure, using a different solvent, or changing the ratio of reactants. Also purifying the reactants in advance sometimes helps.
Other than the comment about catalysts, Jerry's comment can be summarized and extended as "Learn le Chatelier's principle and apply it!" To give more help we need to know what you are doing and what your results are.
This is a very ambigous question. There are lots of possible way to inrease yield from mixing two chemicals together but it would be helpful toknow what two chemicals you want to mix and what product you want to form. Simple things to try :
* Mix different amounts of the two chemicals
* Change reaction conditions (temprature or pressure)
* Use a catalyst
* remove 1 or more products as the reaction proceeds
* Mix different chemicals
* Expose to or remove various forms of light/radiation
* Improve mixing
* stop mixing (allow to stratify)
* bubble air or some other gas through the mixture
*remove air (operte in an intert environment)
I'm sure othr can add lots ore similar suggestions but we need much more information about the system you are studyingto make useful suggestions