Some thoughts on army list composition and the Reinforcement rule. If this rule is in play, then your battle plan will be thrown in disarray if you are not prepared. Thus because of the chance that the reinforcement rule might be in play, the army list should compose of 2 parts of equal or near-equal number of models wise.
1. The first half, the half starting the game. When troops come on as reserve, they do so not as a unit but as individuals and thus will not be able to function as a unit. This must be kept in mind. Missile troops should be considered for this force faction. By starting the game together on the board, missile troops can be grouped as a unit to shoot volleys. There will also be more opportunity to shoot earlier in the game both directly and indirectly. Secondly named heroes should be considered for starting the game. Most named heroes have special abilities thus these ability should be available sooner rather than later. Thirdly, support troops may also be better off starting the game because support troops are best within a unit rather than on their own. Support troops include spearmen, pikemen, or standards.
2. The second half, the half arriving as reinforcement. Reinforcement models are hindered by their delay entry into the fray time wise as well as distance wise. Thus mounted troops, flyers, and faster models are better troops for the reinforcement faction. These models are also typically viewed as higher power troops and will frequently be targeted by missile weapons. Delaying their presence to the battle also delay the number of turns they may be targeted. Similarly, low defense troops, typically cheap troops taken for their sheer numbers, may be better off as part of the reinforcement faction for similar reasons. Some support troops are reasonable reinforcement as well, as the can be directed toward spots on the table that may need combat support rather than opening a new offensive front. Un-named heroes, with their single fate points, make good reinforcement heroes.
3. Rolling for reinforcement. Since the rule stipulates that you roll for one model at a time, it may matter which models are rolled for first and which last. Even if you roll for all similar models at a time, the order of what models are rolled for still matter. Because there is a one in 3 chance your opponent will get to place where your reinforcement enters, it would be better off if he places your least useful reinforcement first, to fill up the least useful reinforcement entry location. The order to roll for are bowmen (if there are any in your reinforcement faction), warriors, warriors with shield, warriors with spear/halberd/pikes, cavalry, infantry standard bearer, cavalry standard bearer, and lastly, heroes.