All plans, whether short-term or long-term, require that you see into the future at least a bit. You have to be able to predict what the chances of success will be with any given plan. With a combination, as long as it isn't too complex, you can often see right through to the end of the captures and threats. Then it's a matter of counting up what is left and assessing the results. A strategic plan is often harder to see through to conclusion before you begin because there are so many things that can go wrong when you don't account for specifics.
A great way to carry out a strategic theme is to use threats and combinations to back up your theme. The following game fragment is a case in point:
1. d4 d5 2. c4 dxc4 3. Nf3 c5 4. e3 a6 5. Bxc4 b5
Position after 5…. b5.
White has completed the first part of his plan from the beginning. He has developed bishop and knight aggressively and controls the center. Meanwhile, Black has only moved pawns. Not a single Black piece is moved yet.
But White is confronted with a dilemma. His bishop is under attack. What to do? It feels wrong to retreat the bishop when White has the only pieces in play and controls the center. The strategic plan demands an attack.
So common sense and tactics come to the aid of strategy. White controls the a2-g8 diagonal. Black's king is the only defender of his f7-pawn, which is on that diagonal. The a8-h1 diagonal also beckons, since Black has an undefended rook sitting there at a8, and White has a queen ready to go to f3. There is a very nice, strong central outpost for White's knight on e5.
Can we make use of all these features of the position? Yes, we can, with the following combination: 6. Bxf7+. White sacrifices bishop for pawn with the idea of bringing the Black king out into the open, vulnerable to a White knight on e5 and a White queen on f3.
6…. Kxf7 7. Ne5+ Ke8 8. Qf3.
White threatens checkmate on f7 and the en prise a8-rook. One of them will have to go.
8…. Nf6 9. Qxa8.
And White has won the Exchange for a pawn, and exposed the Black king as well.
Another way to carry out the same idea is with a different move order: 6. Ne5. White threatens 7. Bxf7 checkmate.
6…. bxc4 7. Qf3
Now White threatens 8. Qxf7 checkmate as well as the en prise rook.
7…. Nf6 8. Qxa8.
And White has won the Exchange.
What if my opponent doesn't go along with my plan?
If your plan is good, this shouldn't matter. A good plan takes all reasonable moves and plans into account. If your opponent tries something unreasonable, chances are it will be bad, and he just did you a favor. But if his move is both good and unexpected, you should take time out to reassess the situation. You might also have resources that you didn't foresee.