In addition to considering the things you can do to speed things along, you might want to consider the things that you should probably avoid.
The bit that sticks out like a sore thumb for me is:
GM: Okay, are you guys going into the forest?
Player 1: I am, yeah.
GM: Okay, but are you going alone? Is anyone else going?
By asking the confirmation questions, GM is stopping Player 1 from going into the forest. And by doing so, actually removing player agency; seemingly in aid of getting the party to enter the forest together.
First, this expects the party to act like a single-minded unit, rather than allowing the players to act as individuals. Second, it slows things down until the party reaches consensus - which in some situations (as you've already observed) can be extremely difficult to achieve.
I would go further to say this is a little unrealistic and clinical; more like what you might see in a movie than real life. Compare the first round of player actions with a group of friends taking a trip to the beach:
Person 1: Ooh there's the ice-cream truck. I'm gonna get me some...
Person 2: Actually stopped 20 meters back to apply some suntan lotion.
Person 3: Has been admiring the "beautiful scenery", and didn't notice what Person 1 said.
Person 4: "Sure, let's go. But I left my wallet in the car, I need to go grab it."
The point is, individuals will tend to do their own things from time-to-time. Let it be and let it flow. Yes it can be a little tricky keeping track of individual locations and events. So it's important to create opportunity for the party to reunite fairly quickly.
Now an alternative way of handling the first round of player actions might be:
GM: Player 1. As you pass the first few trees, you see the forest is a little thicker than you expected. But you manage to find what appears to be a deer trail that you can comfortably walk along. Shortly the path splits into a fork.
Player 1: "Right is always right, so I'll head that way."
GM: (Either based on a quick die roll or simply a decision.) Player 2. You're listening to other guy too intently to notice Player 1 enter the forest. He tells you that the path to the right is best because it leads to a well maintained bridge; and you'll be able to cross the river easily.
GM: Player 3. Yes, we'll assume you did stock up on bread. You pull your night vision goggles out your backpack, and as you look up, you see player 1 pass the first line of trees.
Player 3 I put my pack back over my shoulders and try to catch up.
GM: Player 4. As you finish your routine, you notice a meerkat staring at you quizzically before darting into a tunnel. It dawns on you that no one else noticed. Player 3 is about to enter the forest, and player 2 is still talking to the stranger.
Player 4 "Hurry up Doc! They're going without us!"
Player 2: "Thanks for the info other guy. I've got to go." I call out to the others "Hey wait! I want to cast Detect Evil first."
Player 4: "Sure, go ahead. I'll just mark some trees so you can catch up."
Player 2: "Never mind, let's get going."
NOTE: Player 2 didn't get to cast Detect Evil, but not because of GM. It was her decision based on the game environment. Alternatively, if she still wants to cast it then run after the others, let her do so.
It might not even be relevant, OR....
GM: Player 1. You notice the path seems to stop at a dead-end. You all hear a battle-cry. Player 1. You hear a couple of arrows whizz past your ears, and see a third thud into the ground at your feet.... (Player 2 might catch up in the second or third round of battle. And if Detect Evil was cast, will know whether the enemy is evil or not.)
Next up: Don't get bogged down in minutiae.
The more you fuss about small things, the slower the game progresses. You'll also find that at least some of the players will follow your lead in this regard - making the problem worse.
Unless food shortage is a factor in the game that you want players to role-play to; you don't want to waste time worrying about:
- Exactly when a player bought 2 loaves of bread for 5 coppers.
- When they eat their meals.
- How much of the bread was given to a beggar on the corner.
If you do want to factor the cost of general provisions into a campaign, rather do so using a fixed amount per game week, and assume general provisions are catered for.
Another thing you'll notice from the above exchange is that I played a little loose with timelines. The game-time required for player 1 to: enter the forest, find a path, and follow it to the fork; would be a fair bit longer than the time for player 2 to wrap up conversation. This allows me to "doctor" some information given to the players as I choose.
Third on the list is: Discourage players from role-playing characters that are too destructive for group cooperation.
Let's assume player 1 has a habit of getting himself into trouble by charging forth without considering his companions. And he claims to do so because it's "in-character". Then it's worthwhile trying to persuade him not to do so.
You may see this as going against the objective of player agency. But I think the effort would be justified.
It's obvious that his character's behaviour will annoy the other players. But realistically speaking it would also annoy their in-game characters. In real-life, anti-social people tend to get shunned. And similar is to be expected of anti-social characters in-game. So it would be in player 1's best interests to tone down those traits of his character before the other characters decide to let him meet his fate in the next ambush.
One interesting option (but it could backfire in the wrong group) would be to encourage an in-game, in-character discussion about a problem character's behaviour.
And finally: Avoid creating open-ended scenarios.
As an extreme example, if you say: "You step outside, and the sky is blue". This gives no anchor from which players can base their decision. Any range of responses is possible: "I go to the beach." "I run around screaming 'the sky is falling'." "I recite the Fibonacci sequence in High Elvish."
Obviously this is just another way of saying: "Give your players clear options", as discussed in most of the other answers. So I'll avoid the extra detail, but would like to make an example by mentioning 2 classic computer games.
"Space Quest" and "Leisure Suit Larry"; both were similar kinds of games. A key difference is that right from the start Space Quest had a sense of urgency; a short-term goal. LSL however was very open ended. Both games were very enjoyable, but LSL did need a bit of time to get some momentum going. This was okay as a single-player game. But doesn't work so well in multi-player. Even open world MMO's need the quests and dungeons to give parties clear objectives.
In closing perhaps I should try summarise with answers to the specific questions:
(1) Provide reference points from which players can make decisions. And it helps if players can find in-character motivation to make a specific choice.
(2) a. Be practical. Take short-cut decisions to move things along.
(2) b. (also 3) Let players push things along if they're getting bored. (This is a more positive look at what player 1 might have been doing.)
(3) Discourage players from adopting "in-character" traits that interfere too much with the flow of the game.