Some of the first questions that amateur astronomers have when first observing planets is when to can each planet be observed and how large of a telescope is required to see them.
NEVER look at the sun without proper protection. For those curious about observing the sun, please check out this article.
The best dates for viewing each planet will vary depending on each year for the outer planets of Neptune and Uranus, as will Mercury. This all depends on the orbits of the planets.
For those living in the Pacific Northwest, it is hard to view Mercury because it is only visible for a few days a year on the horizon. More more information about why, check out this amazing article by Ethan Siegal about how hard it is to view Mercury for those living above the 45th parallel.
Shining with a magnitude of -1.9, mercury will appear only dawn and dusk and seem brighter than Sirius. Because the planet is barely far enough away from the sun to. Be visible against the sunlight, the best times to view are 1 hour before sunrise or after sunset. Information about hunting for Mercury can be found here. That said, viewing Mercury will only provide views of the different phases of the planet.
Venus is going to be brighter and easier to find the Mercury. When not near the sun, features in the atmosphere can. Be seen through different colored filters, with the most famous filter being the #47 violet filter. Note, for a #47 violet filter the larger the telescope possible is recommended.
Mars can be seen with 6 inch telescopes as a round orangish-reddish ball. The best time to view Mars is when it is closest once every 18 months. But there is still a plethora of detail that can be seen with 10 inch telescopes or larger.
Saturn and Jupiter
These two planets are the ideal planets for viewing with a telescope, as a telescope of any size will be able to make them out. Most visible during the summer and fall months, the size and magnification of the telescope will determine how big the planets look and how many moons can be seen.
Uranus and Neptune
These outermost gas giant planets will look like small, featureless, bluish or greenish disks through any telescope that an amateur astronomer will be using. They will typically be visible in Fall or Winter.