One of the of biggest questions i come across is when its appropriate to cast spells. As i have said before a spell is an extension of yourself, an extension that grows as you do, and one that needs understanding and the know how. Practice certainly makes for perfect and i do not want to discourage people to not practice magick, but it helps to understand what your putting out in the world before its out there.
Body builders who go to the gym consistently do so because they want to keep the figure they worked hard on, or it feels good to them, and naturally they get stronger each time. Magick is the same concept it takes practice, training, knowing when its time to proceed, and consistently testing your skills.
The truth is there is no real appropriate time for the use of magick its completely defined by the caster. As a young caster i was taught to use the items i had available in the house at the time when the situation deemed fit. Meaning i was taught to trust my instincts on the creation and use my own stuff to obtain my goal. Personally to me there is a symbolic meaning to this, its personal magick. When you get hungry and your at home not wanting to leave but you have enough to make an amazing little meal you do it because the need arises for what you have on hand. Spells work the same way, when the need for witchery arises, just use what you have on hand with what you know.
Trust your instincts, when your mind and body is telling you repeatedly its time, then its time to cast, don't be lazy. Just like at the gym you have to keep at it and practice to get where you want to be. Its better to be both practical and theoretical, to me knowing about something does not give you the means to execute it correctly, nor does the lack of knowing something before executing that in turn. Balance yourself in both skill and knowledge and above all else, trust your instincts in spell timing and casting. After all, you are the beholder.