This is the method and guidelines I go by when I decide to create a thought form for magical purposes. First, plan out all the information for it; everything you want it to be able to do, how it will look etc. Write all this information down on a piece of paper (or in your personal journal) if you wish so you may keep track of it. Then, while you're creating the construct, you can read off all of the features and specifications like a recipe if necessary.
Prepare yourself for the creation process by shifting mental gears with meditation or just general relaxing. You need to be completely focused and ready when you commence any operation.
Then, draw in energy, one type at a time (if you work that way), and concentrate/direct it in accordance with your Will. Just imagine strongly that you're sucking in energy (in whatever phase you need) and breathing it out into an area in front of you where you mold it into the shape you want it; use your hands if you need to at first. Visualize strongly the thing that you're creating, right in front of you. You almost paint the energy where you want it. Push or exhale the energy out of your hands or mind if you must. You might build a construct in sections starting first with one phase of energy (applying it according to its properties), then continuing on with energy in another phase, and then another, until you have completed the task of building one construct. There are many ways to view the process.
Once you have finished making your construct look the way you want with all the features on it you need, then it is time to program it. Imagine that a construct is sort of like a living astral robot that you have created. Now, you must program it so that it can carry out your tasks. All you need to do at this point is to imagine that you are consciously injecting information into it and programming it. If it assists you to do so, you may pretend you are 'breathing' information into the construct; just formulate the program/mental command in your head, and then exhale it into the construct (almost expelling it like in an orgasm from your mind or body- doesn't need to be as intense though). A simple set of mental commands should be sufficient. Things like, "Your job is to protect so-and-so," and, "you are intelligent and know what I wish you to know about the job you are to perform," are usually fine at first. Your first attempts at constructs will likely be simple. As your skills improve, the set of mental commands used to program one with will probably become more complicated. Pay meticulous attention to detail and you'll do fine. As always, your Will or Intention WHILE you are building and programming the construct is what determines how good of a job you do.
Don't forget the time limit! Just put that in as part of your construct's programming. Note: some find it useful to assign names to their creations so that they can be called back to report on progress, or just simply return home. This could also be a useful practice to increase the amount of control you have over a construct. Most people don't give out the names of their constructs without a good reason. It may be a good idea to program yours not to respond to the commands of anyone except you, unless you're making it to assist someone.
Once you've finished creating and programming your construct, dismiss it to perform its task and have confidence that all will go as you've planned.
Don't think of failure while doing anything; such thoughts detract from your effort and scatter the force of your intent. Developing the mindset that failure is not an option and doubts are not possible whenever you commence an operation may be beneficial in keeping your focus; sort of like shifting gears in your mind beforehand every time. I used to build a construct first then program it for the task I wanted it to perform, but you may find it easier to program it while you build it. When I create them now, they seem to spring into life without much effort, being created and programmed simultaneously. With practice, everything is always easier. The more work you put into it, the better it will be. Over time, you'll develop your own style.
Depending on your personal skills, you may or may not perceive your creation visually. It might be that you only feel its presence. This is normal.