A good all purpose increase is a kfb (knit into front and back of stitch). It is not an invisible increase however, so many people prefer to do the M1L (if you want left slanting) and M1R (if you want right slanting). Both have videos on this site, just look in the 'Glossary' tab at the top of this page.
You're right that a YO makes a hole, which isn't always desired, so just use one of the above mentioned.
As for decreases, the K2tog and the SSK are the two most commonly used decreases. The K2tog is a right sloping decrease and the SSK is a left sloping decrease.