In general we do not have a simple way. We have to see the different types of reactions. Understand them. Get the logic in them. You will need to familiarize with all reactions that come in your syllabus. Understand them under different categories, addition, subtraction, oxidation, reduction...
First write the formulas for the reactants and products, that we know. See what elements/compounds would be needed to make the product... It is important to know the structural formula in terms of bonds between C and C as well as C and H..
Then we will add or subtract groups from the formula, decrease or increase bonds correspondingly.
Only unsaturated compounds will be able to get converted into saturated compounds. That is compounds with double bond between two carbons or triple bond, will get converted into single bonded carbon compounds.
you can add halogens to organic compounds like alkynes or alkenes.
alkynes + R => alkenes
alkenes + R => alkanes
R = halogens, hydrogen, groups like OH
when you hydrogenate , ie., add water, it is split into H and OH. two separate groups add to same or different carbons.