Hoyle strategy is both outdated and not entirely complete. When Hoyle was written, the game was to 5 points and included 7's and 8's as part of the deck. That being said, general Hoyle strategy still applies. The largest debate for modern strategy is blocking and when to do so. Modern Euchre goes to 10 points so there are many more opportunities for lone hand to have impact on the game. "Blocking to the left" becomes a sound modern strategy to deal with minor (not at the bridge) blocking.
Hoyle gives thorough probabilities for lone hands. Unfortunately, overlaying the probabilities with Hoyle strategy can point to a different train of thought entirely. If you have not discussed "blocking to the left" with your partner, you should just follow Hoyle strategy anyway. There are pro's and con's to each blocking method so agreement with your partner is needed to be on the same page and prevent double blocking (both partners blocking if they don't have a stopper).
Blocking to the left follows a simple principle that differs from Hoyle strategy. Each player, no matter what position is in charge of blocking only the player on their left. This follows the simple order of calling where the player to the left is the next person to call, then your partner has control if they pass.
Hoyle strategy follows "blocking to the left" for the dealers team, while all blocking falls on 1st seat for the non-dealing team (blocking both 2nd seat and the dealer with the first call of the round).
The largest problem with Hoyle strategy is the fact that 2nd seat is the easiest to call up the turn-up card on off aces, sometimes blocking their own partner. At the same time, the dealer has the most probability of getting a lone hand (having a discard).
The strategy of "blocking to the left" follows more of an instinct for the 1st seat. If they do not believe that 2nd seat has a loner, they should not block. This allows the possibility of the 2nd seat blocking their own partner on a legitimate call, having off aces and being weak in trumps. It also gives 3rd seat much more information to be able to call a block against the dealer (the most probable seat to have a lone hand), rather than 1st seat calling a block blindly (simply on their hand having a stopper or not).
The largest advantage of "blocking to the left" is when the opponents do not know that your team is doing so. 2nd seat can assume that 1st seat has a stopper and can be inclined to call on the turn-up card (blocking their own partner). Even when they have figured out that your team is "blocking to the left", 2nd seat does not know if 1st seat has a stopper, if their partner has a loner or if their partner is going to pass (even though they can get a point according to their hand). 2nd seat, therefore, must give their hand information up to 3rd seat by passing if they cant call or by passing if they think their partner can lone (according to their hand).
This takes away some of the advantage of 2nd seat, being the easiest position to call the turn-up card, by giving a puzzle that requires instinct to overcome. Are they going to block their partner? Is their partner going to pass, even though their side should call?
If 2nd seats hand is such that their partner may have a loner, they have to pass (for it to happen) giving an alert to 3rd seat. Unless 2nd seat has a loner, calling may block their partner. This gives a huge amount of information for the non-dealing team to know when to block or not. 3rd seat then has as much information as possible to call a block against the dealer, where 1st seat (normal Hoyle strategy) would block blindly.
Blocking to the Left Order[]
1st seat on turn-up: 1st seat blocks 2nd seat if their hand is completely junk and they have an instinct that 2nd seat has a loner (keeping in mind that the dealer has a much higher probability of having a loner).
2nd seat on turn-up: Blocks 3rd seat from calling a loner, if the cards and instinct says 3rd seat can call up the turn-up on a loner. Keep in mind that 3rd seat is the hardest seat to call up the turn-up card (especially on a loner) and calling a normal hand may block your partner.
3rd seat on turn-up: 2nd seat passed, they do not have enough power to call a normal call or they believe their partner can lone. Either way, this is the time to decide if the dealer may have a lone hand. If you do not have a stopper, block.
Dealer on turn-up: 3rd seat has a blocker for the turn-up card. Block 1st seat from a lone hand on next.
1st seat on turn-down: Block 2nd seat on a loner, especially if a cross call is in order for 2nd seat.
2nd seat on turn-down: 1st seat did not call next. Block 3rd seat on a loner, especially if a next call is in order for 3rd seat.
3rd seat on turn-down: No one else had a loner or blocked. This is a good indication that the dealer may have a loner in cross (you have the stopper for the turn-up card already).
Note about the Cons[]
The largest con from normal 1st seat blocking is that 1st seat doesn't know if 3rd seat is blocking or making a call. Thus when 3rd seat orders up the dealer, do they play trump or not? The answer is yes. If 3rd seat is calling up, 1st must lead trump (if they have it). If 3rd seat is blocking, a euchre is probably coming anyway.
1st seat has a slight advantage if they were the ones blocking and can lead accordingly to possibly make 3 tricks anyway. The probability window is extremely small for 1st seat to take advantage of this. 1) The block needs to be in error. 2) The 3rd seat needs to have the aces (1st seat may not have blocked if 1st seat had the aces). 3) Leading trump needs to be the exact wrong move to win the tricks (1st seat would have not lead trumps if it blocked anyway).
The second largest con is 2nd seat getting a loner if 1st seat passes. Risking the game on such a probability is acceptable. It can also be agreed that at the bridge, 1st seat will block blindly (normal Hoyle strategy). It is not needed but is sound. Special attention by both teammates is required if switching strategies according to score.
Psychological Cons: When first adapting "blocking to the left" strategy from normal 1st seat blocking, many players cannot make the leap. Especially when they, as 1st seat, have a stopper and 3rd seat blocks. It seems contrary to what their team should be doing but is only contrary to what they are used to. The same probabilities govern 1st seat blocking while 3rd seat has the stopper. The only difference is style of play and what is believed by individual players.
Make sure your partner knows what you are doing and why, before doing it.