What is the best way of paying OVO for my energy?

What kind of account have you set up with OVO? What kind of meter do you have? (I am asking these questions because you have posted your question in the Pay As You Go account section of these pages).

If you have a PAYG meter, then you will pay for your energy in advance, either with a key or card that you insert in your meter after buying credit at an appropriate outlet. If your PAYG meter is a smart meter, then you can also buy credit online.

I suspect that you may, in fact, have a credit account. If that is the case, the best way to pay for your energy is via a monthly Direct Debit as this is the cheapest way to do so. Paying by Direct Debit also allows you to spread the cost of your total usage across the year rather than paying more in winter than in summer. I pay a Direct Debit of £100 per month - between November and April, my total bill was more than £100 but, for the rest of the year, going on past usage, it is likely to be less than £100 - so this balances my costs out. I prefer to pay this way as I have a fixed income. 

Energy prices are set to go up by around 13% on July 1st, so it may be worth looking at one of the fixed price tariffs that OVO is offering. It is predicted that prices are likely to rise again in October - any further than that is just total guesswork. 

Typically, fixed rate tariffs set the cost for each unit of gas and/or electricity and the daily standing charge for each fuel for one or two years. This means that you could fix your cost per unit and per day BUT IT DOES NOT FIX YOUR TOTAL COST. That will vary according to how much energy you use. Fixing charges like this is a gamble, I have only done this for the last two years.

If you set up an online account, depending on the type of meter you have, you can easily check how much you are spending (with a smart meter, you can even see how much energy you have used per day (and half hour periods within that day).