Spidey wrote:However, I cant solve faster than 1min20sec, which is slow.
"Slow" is a relative term (to me at least); it deals with comparisons. You could say you're slow if you compare yourself to someone on YouTube who does twenty second solves. However, you could say you're fast compared to how you used to solve. When you first started, you weren't getting the times that you are now. You've made progress and can be proud about that.
Spidey wrote:Any suggestions?
In general, practice. Do lots of solves, and become more familiar with your solving method. Don't time all of your solves. Do some of them slowly, and try to reduce pauses.
By beginner's method, I'm going to answer as if you mean: cross, first layer corners, second layer edges, last layer (which has its own steps). If you do something else, you can post a response and say so.
For the cross, solve it on the bottom layer, not on the top layer. Keep it on the bottom for the whole solve. This will save you the time that it takes to turn it over. Also, it will allow you see more pieces.
When you're solving the first layer's corners, make sure that you know how to solve each corner the first time you see it. Find a corner, think about where it and how to put it there, then solve it. You don't want to put a corner in wrong then have to take it out. Try to do this without pausing for a long time. You want to eventually be able to see a corner and solve it almost instantly.
For the second layer edges, do the same kind of thing. Don't put any in flipped or in the wrong spot. Aim to solve each one correctly the first time.
For the last layer, make sure that you can recognize each pattern (case) and solve it quickly. You can practice the formulas (algorithms) and try to execute them faster. You can try turning the cube in different ways to do this.
Lastly, figure out ways to turn the cube quickly. You don't need to use your whole hand to turn each layer. The top layer can be turned just using an index finger, for example. This video
shows some ways to turn the cube that might be better than what you are doing now.