This year my friend and I went to GenCon without a plan at all. In fact, that was our plan. Every year had open time for doing random things, but there was some sort of objective. This year the objective was to not have one. We did the whole convention with generics and showing up to places, and quite frankly we had a blast. For those interested in being planless - or just unable to get into the games they want - here is basically how it works.
Step 1: Grab A Bunch of Generics Early On
This shouldn't be a surprise, but to do events with generics you need generic tickets. Most events have a charge of $2/hour (or 1 generic ticket / hour) but some games run a bit more depending on their situation. If going for the whole weekend using generics, I'd recommend grabbing about $40 worth on your first day. It gives you a healthy stockpile that should last you most if not all the weekend.
In getting generics, you're generally better off going into one of the halls where games are played and finding an Event HQ. The lines - especially on the first day in the morning - are short to non-existent (unlike Customer Service and Will Call) and they can sell you generics just fine.
Also, the best part about generics is if you buy too many they're refundable -unlike specific event tickets.
Step 2: Find A Game/Event You're Interested In
The second step is to find a game or event you're interested in. The event finder on gencon.com has decent granularity in its search engine. You can search by category of event, day of event, start time of event, specific game, and/or specific host. You can also filter out full events. So look and find something you want to try. I'd recommend looking for games with open seats, but you can try for full tables too. A lot of times people miss games. Just have a backup in mind for if everyone shows.
Step 3: Show Up Early. Really Early. Ask About Wait Lists
Show up to the room early, and ask if there is a wait list. For games being run by groups, they often have someone by the door to answer questions, feed the GMs water/throat lozenges, and manage tabling/wait lists. Fantasy Flight Games, Baldman Games (they run 5e), and Catalyst have always done a good job with wait lists and getting your name on early is good. Paizo will try to get you in, but their table mustering for events is more ad hoc and they tend to not do waiting lists.
Step 4: You Won't Be Seated Right Away
The thing to remember with Generics is that you not only won't, but can NOT be seated right away. by GenCon rules an event host has to give people 10-15 minutes to show up with event tickets before filling the seat with generics. That means you'll be waiting until about 4:10 to 4:15 for an event starting at 4:00. There is nothing the event hosts or GMs can do about that. And if you try to sit down earlier, and someone with a ticket shows up, you're going to lose your seat.
The best plan here is to be patient, but stay visible and present. You want to hear when they call your name because unlike an event ticket there is no rule about how to use a wait list.
Step 5: Enjoy
Once the event starts, you're just as in as anyone else. Have fun, listen to the person running the game, and do your best to be a good player.
Also, don't be too sad if you can't get into a game you really want to play. Most games have events going every day, so there is always tomorrow. Also, there is always something going on at GenCon so just go find the next thing you want to try.