Hello,What type of transformer you need please?Is your required transformer for 50hz or hiher frequency.However for a efficient transformer the following steps are to be observed:-
1-core material should be of high quality,if you require to make 50hz transformer silicon core is the best choice.
2-the enamelled wire being used should also be of high quality i.e 99.9 copper wire.
3-proper guage of wire according to wattage of transformer should be used otherwise transformer will get hot.turn ratio (np/ns,vp/vs) is to be observed
moreover during winding each layer must be covered with butter paper/other insulated material,after completion insulating varnish must be applied .
If you provide yours specification,then more guidance will be sbmitted.Regards