You can take the bus from Albrook Terminal in Panama City to David. The buses leave almost every hour through the day. The day buses take 7-8 hours and costs $15.25 a person. The night expresses buses take 6 hours and costs $18.20 a person. Traveling to David by bus is probably the safest if you're traveling from Panama City. The buses usually stop in the city of Santiago on the way to David for bathroom breaks and food. Highly suggested that you try some of the food they serve at these stops. Also, you'll find a cart where they sell sweets (mini chocolate eggs and another square treat called cocada), try them out.
The day non-express buses are almost always available and don't require purchasing tickets a few hours in advance. The 3 night express buses, however, sell out from time to time. If you intend on taking one of the night express buses, you can either go in the morning to secure your seat, or you can use the service Panama Bus Tickets (https://www.panamabustickets.com) to reserve your spot without having to make an additional trip to the bus station. They purchase ticket(s) on your behalf once ticket sales open so all you have to do is collect your ticket(s) at Albrook Terminal up to 15 minutes before the bus departure time.
If you are coming from Playa Venao, take a minibus to Pedasí first (around 40 minutes, $1.50). The bus leaves at 07h, 12h and 14h from the main road. If you catch the bus at 7am, you can go all the way until Las Tablas (1 hour 30 minutes, $3). Otherwise you have to catch another minibus to Las Tablas from Pedasí. From Las Tablas take a Bus to Chitré (1 hour, $1.50). From there take a Bus to Santiago and from there you can finally get the bus to David.
By car: There are stop signs at most intersections, but in spanish "Alto" means two things, 1. stop, and 2. HIGH, so there's a joke that some people think "alto" street signs means pass at a high speed. Seriously though, you have to be very DEFENSIVE if you're just driving on the same road, and very OFFENSIVE if you're making a turn, if you're trying to get to the other side of the intersection, etc...
By bus: Most, if not all buses travel to terminal in David. Just stand on the side of the road and wave down a bus when you see it. They'll have written on the window where they go to and where they come from
There's quite a bit to do in David. It all depends on what one likes. There are a few Casinos in the city that you can visit, the two most popular ones are Royal Casino, and the Fiesta Casino (Fiesta is in the Hotel Gran Nacional). There's a few nightclubs to go to, $3 cover, no dress code, $20 for bottle service (Carta Vieja Rum), which is what most people get here. It also depends on what time of year you visit. There's different types of festivals throughout the year, but the best ones are in the beginning of the year, timed with the Carnavales in different parts of the country.
There's plenty of adventure sport and naturalist activities for those so inclined within an hour's drive all over the Province of Chiriqui.
A pleasant day trip from David is to the Los Pozos de Caldera hot springs. These are very undeveloped but in a way this just makes you feel you've strayed from the beaten track a little. To get there, take a Caldera-bound bus from the David bus terminal (USD2) and tell the driver you want to go to the springs. About an hour later, you will be dropped off at a junction where you can walk 2.5km down a paved but bumpy road to the spring entrance, crossing an unusual mini-suspension bridge on the way. From the "Bienvenidos a Los Pozos" sign, walk along the trail as indicated (this can be a little rough, so wear sensible shoes and expect a little mud in the rainy season) until you come to a "private property" sign with a small house beyond. At this point you can pay the owners (USD2) and pass on to the small but pleasantly warm pools beyond. Take care not to leave too late as buses back to David get thin on the ground later in the day. If you do run into problems, you can ask the small restaurant near the junction to call you a taxi, which will cost about USD20.
There are a lot of cheap Panamanian restaurants in David. In most of them you can choose between a plate with chicken, meat or fish and you'll get various side dishes and a drink. Such a plate will cost you around 3,50$. If you just take rice as a side dish it will mostly cost you 2,50$. Most of these restaurants will also serve different Panamanian things for breakfast. You can just choose some things from the counter, usually these pieces of food will cost you a between 20 ct and 1$, depending on what you choose.
You can also eat on the various street food stalls in the center of David, close to the bus terminal. You can get snacks like empanadas, meat or sausage on a stick and a drink for 1$ or less.
Another popular place is "Chobeca's Burgers" which is a Panamanians version of McDonald's. It's cheap, and has nothing to do with burgers. They sell fried Panamanian-type food, try it at least once. Next to the Hotel Gran Nacional (and the Fiesta Casino) is a restaurant called McPato. Now THAT is David's real version of McDonald's from way, way back. The story behind that is that they wanted to bring a McDonald's franchise, but the owner found it to expensive to buy a franchise restaurant, and decided to open his Own. The Mc in the name is obvious, and Pato in spanish means Duck, and Donald is a duck, so the owner figured Mc(obvious)Pato(Donald). Restaurante Chiriqui and Salon Don Pedro are chinese restaurants located within the city. There's really a lot of place to eat at. But if you really are looking for quality and if you enjoy eating well try El Rincon Español, just behind the hotel Ciudad de David. They are one of the best restaurants in David, offering an alternative to fast food.
Carta Vieja, Panama's Rum. No matter where you go in this town to enjoy it's nightlife, you'll see Carta Vieja bottles around you. The clubs offer bottle service, which really, everyone gets. $20 will get you a bottle of Carta Vieja, bottle of coke, and ice, split that up between however many people you go with, and done. If you are the type of person who just likes to have a beer and relax with some friends, El Hangar (The Hangar) is the place to go. It's a drive-thru bar basically. You go, buy your drinks, park your car, and either pump YOUR music, or listen to the music other people are pumpin from their car. It's a nightclub where the patrons are the DJ's basically.
There are many lodging options in the city including many fine and reasonably priced hotels. Many of the hotels are owned by families of Spanish origin, so they have names like Hotel Toledo, Hotel Madrid, Hotel Alcala, Hotel Iberia, Hotel Galicia, etc.
For the backpacking traveler ready for some urban action, clubs, casinos and 24 Hour shopping, consider staying in one of the backpacker hostels especially geared toward the budget traveler.
Tracopa  has the only direct buses from David to San José, Costa Rica at 8:30AM and at 12:00pm noon (costs 21 US, Dec 2015). Travel time is about 8 hours, including an estimated hour at the border and 20 minute food stop in Uvita. The bus also stops on demand, including in Quepos, if you want to get out there and go to Parque Nacional Manuel Antonio, but make sure to tell your driver you want to stop there! The final bus stop is at the Tracopa Ltda station at Calle 5 and Cleto González Víquez in a rough part of San Jose.
Or, you can take your own car/taxi anywhere you want, or fly Air Panama to its many destinations.