For this, you'll need 'real' bread. You want something that is preferably slightly stale, and isn't something like wonder bread. If you hate hard croutons, you'll probably want some sort of rich bread like a challah or potato bread. You don't want a sweet bread since it'll taste funky and burn too easily. The best bread is an ordinary white bread that doesn't have too hard of a crust. You want the crumb or interior of the bread to hold together. A holey bread like a ciabatta is fine, but something that just crumbles as you slice it will make seasoned bread crumbs and not croutons.
Either way, take your bread. Slice it into fairly even pieces. You want to be able to stir the pieces around your fry pan, and you want them to be in an even layer. As long as one plane is fairly even (thickness for example) you should get mostly even cooking. Toss your bread in a fry pan, and add some of the crumbly bits from the slicing.
Now, there's three ways to get the bread seasoned with garlic. One is do crush garlic and add it to the frying bread, but this is uneven in the seasoning. Two is to add the crushed garlic to melted butter, and then pour it on your bread. This may result in burned garlic. Three is the way I prefer which is to slice the garlic into pieces about the thickness of thin cardboard. Plop the slices in a bowl with butter and oil, and heat that in the microwave / in a pan on the stove. Now, you've got garlic flavored butter without the garlic bits to burn since you can hold them back. It's also good to toss dry herbs in the butter.
The other main seasonings is Worchestershire sauce and herbs of some sort. We usually use a generic Italian herb mix. You could use any dry herbs. Fresh ones really don't work right in the dish, but slices of fresh sage might work. Maybe.
Either way, turn the heat on under your bread cubes. You want them to just start browning before you add some butter. You want the butter to encourage the frying and season the bread a little. It will sort of vanish into the bread. Always add a little less than what you think you need as you fry, and you should avoid overly greasy croutons. You can also use olive oil.
Either add your dry herbs as you fry, or have them already in your butter / oil. You want to fry the croutans until they are your desired level of crispness and browning. You can taste them as you go to see how they are cooking. It won't take long at all to fry them to a nice state. You can also salt the bread if you want things to be very salty.
Now, sprinkle Worchestershire sauce over the croutons. You want most of the pan to have dollops of brown, but not to soak the croutons. You may want to back away from the pan or turn down the heat and you do not want to breath the fumes, since there'll be a caustic smell. You can add the slices of garlic and remaining herbs at this time, and stir the mess as the garlic heats and the croutons dry out again. When the garlic is just browning, but isn't black, turn the mess out into a bowl.
So, what you end up with is pretty sad looking. You'll have spotted cubes of browned bread with darker splotches, brown slices of garlic, and the little bits of herbs. The bread crumbly bits will be all browned and hopefully not burnt. However, it will smell very good thanks to the rich smell of the garlic and herbs, and the faintly acidic smell of the Worchestershire sauce. If you're scared of using the sauce, feel free to leave it out, but I associate it with 'proper' croutons in my mind.
You can use the croutons in any soups, on bread, and of course in salads. A simple soup could be rinsed canned black beans, bit of garlic, a hint of sherry, and heated in a pan. Run it in a blender / food mill / beat on it with a potato masher if you really want to be fancy. Chopped ham and croutons with that is a lovely meal.