Effective. Efficient. Effectual. Efficacious

We use effective to describe something that gives you the results you want:
Taking this tablet is a very effective cure for travel sickness.
In this light, the camera is more effective if you use the flash.
Services need to be more effectively organised than they are at present
Effective

An effective public transport system
To function effectively
The effectiveness of computers as an educational tool
The use of effective

Effective means having a particular role or result in practice, though not officially or in theory.
Virtual
Essential
Practical
They have had effective control of the area since the security forces left.
The restructuring resulted in an effective increase on fares.
Effective / practical

producing a striking impression;
An effective entrance
Effective/ impressive

The company launched a highly effective advertising campaign.
Extremely / highly effective

What is the most effective way to control crime?

Exams are not the most effective method of assessing students’ abilities.

Is reducing the speed limit an effective means of reducing accidents?

The most effective solution to traffic congestion is to build more roads.

The country has a simple but effective welfare system

Welfare is a type of government support intended to ensure that members of a society can meet basic human needs such as food and shelter. Social security may either be synonymous with welfare, or refer specifically to social insurance programs, which provide support only to those who have previously contributed (e.g. most pension systems), as opposed to social assistance programs, which provide support on the basis of need alone (e.g. most disability benefits).
Welfare

We use efficient to describe something or someone that works in a quick and organised way
If something or someone is efficient, they are able to do tasks successfully, without wasting time or energy
The new online banking system offers a convenient and efficient way to check your account.
It could be an exceptionally efficient and economical way to make buildings more comfortable and energy efficient.
I have always known James to be highly competent and efficient in all aspects of his job.
Efficient

performing or functioning in the best possible manner with the least waste of time and effort; having and using requisite knowledge, skill, and industry; competent; capable
a reliable, efficient secretary
I have always known James to be highly competent and efficient in all aspects of his job.
Efficient / competent

The factory is modern and highly efficient.
Extremely/ highly efficient

Email is an efficient way of contacting a large number of people

The railways used to provide a cheap efficient method of travel

The tram is a very efficient means of transport.

We need a more efficient system for collecting money.

We must work towards the more efficient use of all natural resources.

More efficacious treatments may soon be available