Simply put, there are many ways to organize thoughts, ideas and themes.  Pick an organizational pattern that is right for your presentation.  Here are a few choices:

• Sequential/chronological: Does your presentation move through a series of points that can be organized in a sequential or chronological pattern?  If so, do not attempt to jump around and explain your points non-sequentially or your audience can easily get lost.  If the points you wish to make or the story you have to relate occurred one at a time, stick to the chronology.  Your audience will follow right along with you.  It’s a lot like that two-page instruction manual that comes with your new electronic device and always goes through each step in sequential order.  Some topics just require this form of organization to be understood: What happened first? What happened second? Then what happened?  And sometimes you can start with the end and work your way back, but you definitely can’t skip around if a topic really needs a sequential presentation.
• Categorical/topical:  Your main points may be most easily presented by category or topic.  Clearly state what you’re going to be covering during the course of the seminar or speech, give the audience a means to remember it and then proceed exactly as you described.  (For heaven’s sake don’t tell them you’re going to talk about Earth, Wind and Fire and then present it as Fire, Wind and Earth.  Stick to the categories you establish from the get-go.)
• Compare and contrast: When making comparisons, be sure the comparisons are valid.  Apples are not oranges.  Don’t make the mistake of mixing up the two.  If you want to compare raising a child to raising a domestic animal, you run the risk of alienating the parents in the room.  (Or the pet owners, for that matter.)  But if you hit upon a comparison that works, by all means use it.  The same rule applies to contrasts.  Baseball is similar to football in that both are sports, both use a ball and both employ a points system.  In that way, you can compare the two.  But there are also many ways you can contrast them and examine the differences.  (George Carlin did this famously and to great effect.)  Using comparisons and contrasting examples is a wonderful way to hammer home an important point.
• Problem — solution:  This is a simple way to both organize and present a speech cleanly and with little digression:  Set up a problem and then offer a solution (or several solutions) to that problem.  Be sure that the problem is one common to most members of the audience (the less obscure you can be the better) and try to offer novel or clever solutions rather than merely obvious ones.  You don’t want to talk down to them.  Within the problem — solution framework, you might, for example, discuss the causes and impacts of problems (such as gambling compulsions or addictions), review past or outmoded solutions that have failed in the past and, finally, provide a new or time-tested solution that is most likely to work.