So you've watched all of New Who, and you want more: more Doctors, more companions, more time travel, more adventures. You're in luck! Classic Who is where it all began. You've got 26 years worth of Doctor Who to enjoy. So let's get started!
Note: We're assuming you've watched at least some Doctor Who. If you're looking to get into the show, you probably don't want to start with Classic Who—check out our Introduction to Doctor Who for more information.
You're familiar with Doctor Who at the height of its success, with amazing sets and miraculous special effects. New Who has a huge budget, entirely due to the fact that only it's so popular. But it only became popular after being on air for a long time. Classic Who never had the same awesome sets or special effects (it was the 70s, after all!) that you may have come to expect from New Who. So don't expect the same production value. Of course, Doctor Who has always been lucky enough to have great good writers and fantastic actors.
Many guides to Classic Who will warn you about shaky sets, or poor pacing. Here, at HelpMeWatchWho, we're not going to do that. To quote Reddit user JoGrant: "The danger of people telling you what's good/what's not/what's well paced/what era has bad special effects etc. etc. etc. is that they colour your expectations of that era of the show and those fears you have can become self-fulfilling (e.g. you're told that the first Doctor's era is slow, and so all you can think about when you watch him is "wow, this is slow", which prevents you from getting immersed in it and deciding for yourself what you think of the pacing). Inherited fan wisdom can be destructive of one's enjoyment of the show."
So yes, there will be times where the show is very, very slow, or the special effects are simply awful. Early episodes are black and white and grainy. The Doctor Who Restoration Team has done an amazing job of improving production values via editing and other wizardry to provide the best possible experience, but it's still not perfect.
The format of Classic Who is very different from that of New Who. In New Who, each story is told in one episode. Occasionally, there are two or three part episodes, but they're rare. Classic Who is very different.
One story in Classic Who is called a "serial." A serial is made up of several episodes—usually four, but sometimes as few as two or as many as ten. For the first 25 serials of Classic Who, each episode had an individual name within the serial title. For the vast majority of the show, however, the episodes are just named with the serial name and the part number.
After the show was cancelled in 1989, there was a short-lived attempt to revive it in 1996. A made-for-TV movie was made, titled simply Doctor Who. Frequently, it's referred to as The TV Movie (or TVM), Doctor Who: The Movie, or occasionally The Enemy Within.
The first six season of Classic Who are missing a lot of episodes. "Missing" refers to episodes that are lost to time; nobody has a copy of the episode, not even the BBC. Why? In the 60s, when Doctor Who was first created, the BBC had a policy of erasing tapes after episodes had aired so that they could be reused. Most stories in the first six season were erased like this.
A lot of previously missing episodes have since been found, in all sorts of places. In some cases, the BBC did keep a copy. Sometimes they sent tapes to foreign boradcasters, who kept the tape. Fans at home occasionally took footage of crucial moments. Many episodes have been recovered by various methods.
However, a lot of episodes are still missing. With every passing year, the chances of finding these episodes decreases. But you can still experience missing episodes in other ways. Some episodes have animated realeases. Others have reconstruction made from what clips we have, photos, and linking narration. Many stories were novelized when they first aired. Though the episodes themselves are missing, the story that they tell is not.
Classic Who has a lot of amazing stories, and a lot of boring stories. Some have direct connections to New Who, some are completely ignored or overlooked. Maybe you only want to see the stories that are truly important or incredibly awesome. Maybe you just want to learn more about the Daleks, or the Cybermen, or the Autons. Good news: Classic Who doesn't really require you to have watched every episode. The stories are more or less self-contained. So go ahead and watch whatever you want, in whatever order you want! For lists of recommended episodes, check out Must Watch Doctor Who Episodes, Doctor Who Recomended Viewing List, or Old School Doctor Who Episodes that Everyone Should Watch.
Spearhead from Space is a fun introduction story featuring a new Doctor and the Autons. Sound familiar? It has some parallels to Rose, which is a nice reminder of the fact that everything is, in fact, one show. It introduces the (relatively few) plot elements necessary to understand future episodes and nicely sets up the Doctor's future adventures with U.N.I.T. It's near the beginning of the show, so you won't miss much, but you're past all the black and white episodes and all the missing episodes. Plus, it's the only Classic Who story to be released on Blu-Ray, so you can watch it in high quality.
Tom Baker (the Fourth Doctor) is regarded by many to be the best Doctor ever. He's a great actor, but he was lucky to also have great companions and very strong writers. The Ribos Operation is the first in the Key to Time plot arc, which features some fun adventures and characters. It's certainly a high point of the show, and several fan-favorite episodes come soon after.
Where else to start but the beginning? An Unearthly Child was the start of it all. If you start here, you'll miss nothing, and you'll experience everything spoiler-free. As far as pilots go, it's pretty amazing, and the following serials are classics. However, you may be stymied by production values and frequent missing episodes.
All we can say is, no matter where you start, if you enjoy what you're watching, keep watching. If you don't, move on to another episode.